Why Food That's Safe for Us Can Kill Animals?

Most of us treat "food" as a universal category: if it's fit for a human, surely it's harmless to a pet. Biology disagrees. Every species carries a toolkit of enzymes, receptors, transporters and organs shaped by millions of years of eating a particular diet. When a molecule meets a body that never evolved to handle it, a treat becomes a toxin.

The ASPCA Animal Poison Control Center (APCC) passed 5 million animal exposure cases in 2025, and human food and drink ranked second on its list of the top ten toxins of 2024. Grapes and raisins alone generated more than 9,300 cases in 2025 by late July.¹

1. Chocolate: Same Molecule, Different Clock

The toxin: theobromine, with a smaller dose of caffeine. Both are methylxanthines.

How it works: Theobromine and caffeine competitively block adenosine receptors, the body's built-in "slow down" signals. Blocking them overstimulates the nervous system, speeds the heart and increases urination.² In people, that's the gentle lift of a cup of cocoa. In dogs, it can mean hyperactivity, tremors, arrhythmias and seizures.

Why dogs are vulnerable: it's about time, not chemistry.

• Theobromine's half-life in dogs is about 17.5 hours (caffeine's is about 4.5 hours).²
• In humans, a classic study measured a mean of 6.1 hours; veterinary references give a human range of roughly 6–10 hours.³⁴

Dogs also "recycle" the compound. After the liver processes it, some is excreted in bile and reabsorbed from the gut (enterohepatic recirculation),² and methylxanthines can even be reabsorbed across the bladder wall.⁵ So each bite piles on top of the last before the body has cleared it.

Not all chocolate is equal:⁶

Type	Theobromine (approx.)
Cocoa powder	~20 mg/g
Dark / plain chocolate	~15 mg/g
Milk chocolate	~2 mg/g
White chocolate	~0.1 mg/g

Dose and effect. From ASPCA APCC experience: mild signs at about 20 mg/kg of theobromine plus caffeine, severe signs at 40–50 mg/kg, and seizures at about 60 mg/kg.⁷ Veterinary proceedings list 100 mg/kg as a minimum lethal dose.⁴ Put it together and less than 100 g of plain chocolate, roughly one bar, may be fatal for a 10 kg dog.⁶

A worked example. A 5 kg terrier eats a 50 g bar of dark chocolate: 50 g × 15 mg/g = 750 mg of theobromine, or 150 mg/kg. That's past the seizure threshold and into the lethal range. The same bar of milk chocolate (about 100 mg in total) works out to about 20 mg/kg: the "mild signs" zone. White chocolate is mostly a fat-and-sugar problem.

What it looks like. Vomiting, restlessness, excessive thirst and frequent urination come first, progressing to a racing heart, tremors and seizures in severe cases. Because the half-life is so long, signs can persist for up to 72 hours.⁷

Treatment. There is no antidote. Vets induce vomiting if ingestion was recent, give activated charcoal (often repeated, to break the recycling loop), run IV fluids to speed excretion, and control heart rhythm and seizures.²

Cats? Cats are susceptible too, but because they can't taste sweetness (see section 5), they rarely eat chocolate voluntarily.⁸

2. Grapes and Raisins: A 20-Year Mystery Solved in the Baking Aisle

The history. Around 1989, toxicologists at the ASPCA APCC noticed a pattern in their database: dogs that ate grapes or raisins were developing acute kidney failure.⁹ In 2001 the APCC became the first to report the link.¹⁰ A 2005 review of 43 affected dogs (1992–2002) found only 53% survived.¹¹

But the cause was a mystery. Mould toxins, pesticides, heavy metals, tannins, too much sugar: all were suspected, none proven.¹² Stranger still, there was no clear dose-response. Four or five grapes were enough to cause kidney injury in a dachshund, while other dogs ate up to a kilogram of raisins with no symptoms.¹²

The breakthrough came from the kitchen. ASPCA toxicologists noticed that dogs who ate cream of tartar (potassium bitartrate, a baking ingredient) or tamarind showed the same vomiting, kidney failure and microscopic kidney lesions as grape-poisoned dogs. The common denominator was tartaric acid. Their 2022 case series in the Journal of Veterinary Emergency and Critical Care named it the likely toxic component in grapes, raisins and tamarinds.¹³¹⁴

It even explains the randomness. Tamarind contains about 8–18% tartaric acid; grapes up to about 2%, typically 0.35–1.1%,¹⁵ and the amount varies with variety, ripeness and growing conditions.¹⁶

Why dogs? According to the Merck Veterinary Manual, dogs excrete organic acids poorly because they lack organic acid transporters that other species have, so tartaric acid accumulates in the cells of the proximal kidney tubules.¹⁶

Risk threshold. Merck's rule of thumb: more than one grape or raisin per 4.5 kg (10 lb) of body weight may contain enough tartaric acid to pose a risk.¹⁶ Zante currants and sultanas count too.

What it looks like. Vomiting or diarrhoea within 6–12 hours (often with grape pieces visible), then lethargy, loss of appetite, thirst and dehydration. Kidney values rise, and the dog may progress to producing little or no urine within 24–48 hours, generally within 72 hours.¹⁶

Treatment. For recent ingestions above the level of concern, the ASPCA recommends inducing vomiting followed by IV fluid diuresis for 48 hours.¹⁰ Dogs that stop producing urine have a much worse outlook.¹¹

3. Xylitol: The "Healthy" Sugar That Hijacks a Dog's Pancreas

Where it hides. Xylitol, also labelled "wood sugar", "birch sugar" or "birch bark extract",¹⁷ sweetens sugar-free gum, mints, some peanut butters, baked goods, toothpaste, and even some human liquid medicines.¹⁸

In people it's nearly harmless. It barely stimulates insulin; eating more than 130 g a day mainly causes diarrhoea.¹⁹

In dogs it flips a switch. The FDA explains that dogs absorb xylitol quickly and it triggers a potent release of insulin from the pancreas, crashing blood sugar within 10 to 60 minutes.²⁰

How potent? In one study, peak insulin after dogs ate 1 g/kg of xylitol was six times higher than after the same dose of glucose. Blood sugar fell to about 50 mg/dL within an hour instead of rising.²¹

An accidental discovery. The effect was first noticed in the 1960s, when researchers were testing intravenous xylitol as an energy source for parenteral nutrition and found it caused a dose-related insulin release in dogs.²¹

The numbers:

• More than ~0.1 g/kg can cause hypoglycaemia; more than ~0.5 g/kg can cause acute liver failure.²²
• One piece of gum or one mint typically contains 0.22–1.0 g, so a single piece may cause hypoglycaemia in a 4.5 kg (10 lb) dog.²³

Two waves of damage. The first is low blood sugar: vomiting, weakness, wobbliness, collapse, seizures, coma.²⁴ The second, at higher doses, is liver necrosis with bleeding problems. In an eight-dog case series, three were euthanised, two died and two made full recoveries.²⁵ The mechanism of liver damage is still unclear; leading hypotheses are ATP depletion or reactive oxygen species produced as xylitol is metabolised.²⁴

Treatment. Treat with rapid decontamination and intravenous dextrose until the dog can regulate its own blood sugar, typically over 12–48 hours. Activated charcoal binds xylitol poorly and isn't recommended.²³ Because liver injury can be delayed, liver values are often rechecked days later.²⁶

4. Onions, Garlic and Chives: Rusting Red Blood Cells

The family. Onion, garlic, leek, shallot, chives and Chinese chives all belong to the genus Allium.

The chemistry. Their sharp taste comes from sulphur compounds that are released and transformed when you chop, chew or cook them.²⁷ In dogs and cats, several of these, including n-propyl disulfide and a family of thiosulfates, act as oxidants.²⁸ Researchers at Hokkaido University isolated sodium n-propylthiosulfate from boiled onions and showed it causes Heinz-body anaemia in dogs; a related compound, sodium 2-propenyl thiosulfate, was later found in boiled garlic.²⁹³⁰

How the damage happens. Oxidants attack haemoglobin inside red blood cells. Damaged haemoglobin clumps into lumps called Heinz bodies that stick to the cell membrane; the cells become fragile and are destroyed, causing haemolytic anaemia. Oxidised haemoglobin also becomes methaemoglobin, which carries oxygen poorly.³¹

Why cats and dogs?

• Cats are the most susceptible species, followed by dogs.³²
• Cat haemoglobin is about two to three times more susceptible to oxidative damage than that of other species, and dog red cells have low catalase, an antioxidant enzyme.³³
• Some dogs with a hereditary trait of red cells high in glutathione and potassium are even more susceptible.²⁹

How little it takes. Toxicosis has been reported in cats after less than a teaspoon of cooked onion, or 5 g/kg of raw onion. Concentrated forms like dehydrated flakes, onion powder and dry soup mixes are the most dangerous.³²

Cooking doesn't help. Cooking, drying and processing don't eliminate the toxic effect. Reported cases include baked garlic, onion soufflé, butter-cooked onions and Chinese steamed dumplings containing Chinese chives and garlic.³⁴

The trap: delay. Heinz bodies and methaemoglobin rise within 24 hours, but visible anaemia (weakness, pale or yellow gums, collapse, dark urine) may take several days,³² long after anyone remembers the leftovers.

Treatment. Decontamination if recent, then supportive care; severe cases may need oxygen and blood transfusion.³²

5. Cats and the Missing Genes

Cats are hypercarnivores, and their genome carries the scars.

A missing detox enzyme

Most mammals use an enzyme called UGT1A6 to attach glucuronic acid to certain compounds (glucuronidation), making them easy to excrete. In 2000, researchers showed that in the domestic cat this gene is a pseudogene: wrecked by five harmful mutations and not expressed. The same mutations appeared in unrelated cats and mostly in a wild margay too.³⁵

A 2011 study dated the loss to between 35 and 11 million years ago; every living cat species has the broken gene. Out of 22 other carnivore species tested, only the brown hyena and the northern elephant seal also had broken UGT1A6, and every species with the defect was a hypercarnivore (more than 70% animal matter in the diet).³⁶

The logic: animals that never eat plants rarely meet plant compounds, so natural selection stops maintaining the tools to clear them.

The price shows up in our medicine cabinet. Glucuronidation of acetaminophen (paracetamol) is about 10-fold lower in cats than in dogs and humans.³⁷ When the normal pathways are overwhelmed, acetaminophen is converted into a toxic metabolite, NAPQI, which damages haemoglobin and red blood cells. Cats can show signs at doses as low as 10 mg/kg,³⁸ a fraction of one human tablet for a 4 kg cat. Aspirin, too, must be dosed far less often in cats.³⁷

A missing sweet receptor

Mammals taste sweetness with a receptor built from two proteins, T1R2 and T1R3. A 2005 PLoS Genetics study found that the cat's Tas1r2 gene has a 247-base-pair deletion and multiple stop codons: it's a pseudogene, and the same defect appears in tigers and cheetahs.³⁹ Cats simply cannot taste sugar. Chickens also lack a functional Tas1r2.⁴⁰

6. Avocado: Guacamole for You, Heart Failure for a Budgie

The toxin: persin, a fatty-acid-like compound found in the leaves, fruit, seeds and bark. It was already known as an antifungal agent before it was linked to animal poisoning.⁴¹⁴²

Who's at risk. Merck lists cattle, goats, horses, mice, rabbits, guinea pigs, rats, sheep, budgerigars, canaries, cockatiels, ostriches, chickens, turkeys, lemurs, aye-ayes and fish. Caged birds seem most susceptible; chickens and turkeys seem more resistant.⁴³ Dogs appear relatively resistant compared with birds and livestock.⁴⁴

What it does. Persin causes death of heart muscle cells in birds and mammals and sterile mastitis in lactating mammals. In lactating mice, purified persin caused mastitis at 60–100 mg/kg and heart damage above 100 mg/kg. Goats develop severe mastitis after eating 20 g of leaves per kg and heart injury at 30 g/kg.⁴³ How persin damages the heart is still unresolved.⁴¹

The evidence:

• 1989: Mashed avocado was given to 8 budgerigars and 8 canaries. Six budgerigars and one canary died within 24 to 47 hours, with swelling of the chest and fluid around the heart.⁴⁵
• Ostriches: 9 of 120 ostriches in an avocado orchard died of congestive heart failure within 96 hours of eating leaves and unripe fruit; feeding trials reproduced severe heart damage.⁴⁶
• May 2026: Agriculture Victoria in Australia reported domestic ducks dying 6–7 hours after a feed that included six whole avocados. Avian influenza was ruled out.⁴⁷

Variety matters. Guatemalan-type avocados and their hybrids are toxic; the Mexican type is not known to cause poisoning.⁴⁸ Hass and Fuerte, common supermarket varieties, are both considered toxic.⁴⁴

7. Macadamia Nuts: A Mystery With a Happy Ending

Dogs are the only species in which poisoning has been reported, and the toxin and mechanism are still unknown.⁴⁹ Theories include a compound specific to dogs, processing contaminants or mould toxins.⁵⁰

What it looks like. In a review of 29 ASPCA cases, signs appeared within 12 hours in 79% of dogs: weakness (especially in the hind legs), depression, vomiting, wobbliness, tremors and fever. The mean amount eaten was 11.7 g/kg. When four dogs were experimentally given 20 g/kg, they couldn't stand 12 hours later and ran temperatures up to 40.5 °C.⁵¹ Signs have appeared at about 2.4 g/kg.⁴⁹ With nuts weighing roughly 2.6–5 g each,⁵² a 10 kg dog could be affected by around five to ten nuts.

The good news. All dogs, field cases and experimental ones, recovered within one to two days, treated or not.⁵¹ The caveat: macadamias are often coated in chocolate or baked into cookies with raisins, which adds a far more serious problem.

8. Raw Bread Dough: A Brewery in the Stomach

Baked bread is fine for pets in small amounts (as long as it isn't raisin bread). Raw yeast dough is a different story.⁵³

Two problems at once. A dog's stomach is warm and moist, an ideal incubator. The yeast keeps fermenting, making the dough expand and producing carbon dioxide and ethanol.⁵⁴

1. Bloat. The swelling dough stretches the stomach, compromises blood flow to the stomach wall and makes breathing difficult; in susceptible breeds it may trigger gastric dilatation-volvulus (twisted stomach).⁵⁴
2. Alcohol poisoning. Ethanol is absorbed into the blood, causing drunkenness, low blood sugar, metabolic acidosis, low body temperature, depressed breathing, and potentially seizures and death.⁵⁴⁵³ Death is usually caused by the alcohol, not the bloat.⁵⁴

Telling detail. Ethanol irritates the stomach and triggers vomiting, but also relaxes the muscles that protect the airway, so the risk of inhaling vomit is high.⁵³

Reassuring detail. A dog that eats a packet of dry yeast on its own isn't at risk of alcohol poisoning: yeast needs sugar to ferment.⁵³

9. Hops: The Homebrewer's Hidden Hazard

Hops (Humulus lupulus) give beer its bitterness. Fresh, pelleted or spent (used) hops can trigger a life-threatening, runaway rise in body temperature in dogs, resembling malignant hyperthermia.⁵⁵

The history. A 1997 JAVMA report described five dogs that ate spent hops; four were Greyhounds, and four of the five died despite aggressive treatment.⁵⁶ Later case reviews were more hopeful: 77% of 71 dogs survived with intensive care,⁵⁷ and 95.2% of 177 dogs survived in a 2023 study, although some still developed fatal hyperthermia.⁵⁸

Who's at risk. Any dog, but breeds prone to malignant hyperthermia, such as Greyhounds, Labrador Retrievers, Saint Bernards, pointers, Dobermans, Border Collies and American Cocker Spaniels, may be at higher risk.⁵⁹ Merck notes there are no reports of hops poisoning in other species.⁶⁰

What it looks like. Signs can start within 30–60 minutes or take up to 12 hours: heavy panting, restlessness, a racing heart, vomiting, very high temperature, tremors and seizures.⁵⁵ One UK Labrador reached 42.7 °C despite active cooling.⁶¹

Mechanism: unknown. Leading suspicion is that compounds in the plant uncouple oxidative phosphorylation, the cell's energy production, turning muscle energy into heat.⁶⁰⁵⁶

Treatment. Decontamination, aggressive cooling, IV fluids, and dantrolene, a muscle relaxant used as an antidote for malignant hyperthermia.⁶⁰

Where dogs find it. Spent hops dumped in compost or spread as garden fertiliser seem especially attractive to dogs.⁶¹

10. Salt and Homemade Play Dough

Salt is essential for every animal. Too much is toxic for every animal too, but the margins differ.

The numbers. Merck gives an acute oral lethal dose of about 2.2 g/kg for pigs, horses and cattle and about 4 g/kg for dogs, with signs possible at 2–3 g/kg. Sheep are the most resistant, at about 6 g/kg.⁶²

The surprising culprit: homemade play dough. A common recipe uses 2 cups of flour, 1 cup of table salt and half to one cup of water,⁶³ making it salty, tasty-smelling and easy for a dog to eat in quantity. Christmas salt-dough ornaments carry the same risk.⁶⁴ In one case, an eight-year-old Airedale Terrier ate a salt-flour sculpting clay, had 45 minutes of continuous seizures, and died despite aggressive treatment; his serum sodium was 211 mEq/L against a normal range of 145–158.⁶⁵

How it hurts. Excess sodium pulls water out of cells, including brain cells, causing vomiting, thirst, wobbliness, tremors, seizures and coma. Correcting it too fast is also dangerous: a rapid drop in sodium can send water rushing back into brain cells and cause cerebral oedema.⁶³⁶⁶

Other sources: seawater (dogs playing in the ocean without fresh water), rock salt, paintballs, and salt once used to make pets vomit, a practice no longer recommended.⁶²

11. Milk: The Cat-and-Saucer Myth

Not every food on this list is lethal. Milk is an example of an everyday food that simply doesn't suit every species.

Like most mammals (and most adult humans), cats lose much of their ability to digest lactose after weaning. A 1993 study measured cat intestinal lactase activity falling from about 96 units in newborns to about 13 by six weeks and about 7 in adults, though a few adult cats retained high activity.⁶⁷

Undigested lactose travels to the colon, pulls in water and is fermented by bacteria, causing diarrhoea, gas and sometimes vomiting, usually within 8–12 hours.⁶⁸ It's a matter of dose: research found adult cats tolerated about 1.3 g of lactose per kg but not 4.5 g/kg.⁶⁹ A splash is usually tolerated; a saucer a day may not be. Chronic diarrhoea can lead to dehydration.⁷⁰

12. Rabbits, Hamsters and Guinea Pigs: Small Bodies, No Exit

Pocket pets have their own rulebook. Their problems are less about one exotic toxin and more about plumbing: what goes in, can't come back out.

No reverse gear

When a dog eats something bad, it can vomit. Rodents can't. A 2013 PLoS ONE study tested members of all three major rodent groups, including rats, mice, voles, beavers, guinea pigs and nutria. Classic vomit-inducing drugs produced no retching or vomiting in any of them. The researchers found anatomical limits, such as a weaker diaphragm and a stomach shaped poorly for pushing contents back up, but concluded that the most likely reason is a missing brainstem circuit: the inability to vomit seems to be a general property of rodents.⁷¹ Rabbits are widely reported to be unable to vomit as well.⁷²

That has two consequences. Vets can't simply induce vomiting to empty a hamster's or rabbit's stomach. And anything that disturbs the gut has to be dealt with all the way through it.

A fermentation vat that sugar can spoil

Rabbits (and guinea pigs and chinchillas) are hindgut fermenters. Their large caecum is a vat of microbes that ferment plant fibre into volatile fatty acids, which supply about 40% of a rabbit's calories. Rabbits then eat special soft droppings, called caecotropes, to absorb the nutrients the microbes make.⁷³⁷⁴

This system runs on fibre. Merck recommends about 15% crude fibre, easily provided by unlimited grass hay;⁷³ the University of Illinois advises that more than 75% of a rabbit's diet should be grass hay.⁷⁴ Starchy and sugary foods do the opposite. Carbohydrates suppress motilin, a hormone that keeps the gut moving, and excess starch reaching the caecum feeds harmful bacteria such as Clostridium spiroforme, which produces a potent toxin.⁷³

The result can be enterotoxaemia: sudden, severe diarrhoea and death within 48 hours. In Merck's words, "a rabbit may look healthy in the evening and be dead the next morning."⁷⁵ The milder, far more common version is gastrointestinal stasis, a slowdown of the gut seen in up to 25% of rabbits brought to vets.⁷⁴

So a biscuit, a cracker, yoghurt drops or a handful of breakfast cereal, harmless to a child, are poor food for a rabbit. As the House Rabbit Society puts it, an adult rabbit can digest the fructose in fruit, but the sugar in a candy bar can make it sick.⁷⁶

The medicine-cabinet trap: antibiotics

Here's the most surprising entry in this whole article: some of the most common antibiotics in human medicine can kill rabbits, hamsters and guinea pigs.

Merck lists clindamycin, lincomycin, erythromycin, ampicillin, amoxicillin-clavulanate and cephalosporins as drugs that shouldn't be given to rabbits by mouth.⁷⁷ Lincosamides (clindamycin and lincomycin) are contraindicated in horses, guinea pigs, hamsters, rabbits, chinchillas and ruminants because they can cause lethal disruption of gut bacteria.⁷⁸ The veterinary clindamycin label itself warns: do not give to rabbits, hamsters, guinea pigs, horses, chinchillas or ruminating animals.⁷⁹

Why? These drugs wipe out the friendly gram-positive bacteria that keep a herbivore's gut in balance, leaving room for toxin-producing clostridia, including C. difficile, to take over.⁸⁰ In one experiment, four of six rabbits given a single intravenous dose of clindamycin died or had to be euthanised.⁸¹

The hamster's strange place in medical history. Lethal enterocolitis in hamsters given lincomycin was reported in 1968. By 1977, clindamycin-associated colitis in hamsters had become a laboratory model for the antibiotic-associated colitis seen in human patients.⁸² The same drug that can trigger C. difficile diarrhoea in people is simply far more dangerous for an animal whose whole digestion depends on gut microbes.

Penicillins given by injection under a vet's direction are generally safe for rabbits.⁷⁷ The lesson is about the route and the drug, and a reason never to share leftover human medicine with a pet.

Foods to keep out of the hutch

Merck's list of plants and foods that are toxic to rabbits includes apple seeds, raw beans, sweet potato, rhubarb leaves, potato eyes, shoots and green parts, and chocolate; fruit, alfalfa and some brassica greens should be limited.⁸³

• Avocado: rabbits and guinea pigs are on Merck's list of susceptible species.⁸⁴ The ASPCA warns of gastrointestinal signs, potentially life-threatening heart and lung problems, and painful mastitis in nursing does.⁸⁵ A 2019 report in Toxicon described acute heart failure in rabbits that ate avocado leaves.⁸⁶
• Chocolate: rabbits are less sensitive than dogs to chocolate's effects on the heart, but more sensitive to its gastrointestinal effects, which is serious given their anatomy.⁸⁵
• Salt: sodium poisoning has been reported in a pet rabbit.⁸⁷
• A myth worth checking: iceberg lettuce. It's often said to be dangerously "sedating" for rabbits. The evidence is thin; the better reason to skip it is that it's mostly water and offers little nutrition.⁸⁸

Hamsters face most of the same hazards. Chocolate, caffeine, onion and garlic, avocado, fruit pits and apple seeds are commonly flagged as unsafe. Their tiny body size means a small amount matters, and because hamsters stash food in their cheek pouches and bedding, a problem can go unnoticed for hours.⁸⁹

Guinea pigs: the rodent that shares our weakness

Most mammals make their own vitamin C. Humans, other primates and guinea pigs can't: we all lack the final enzyme in the pathway, L-gulonolactone oxidase.⁹⁰ In 1992, Japanese researchers showed that the guinea pig still carries the gene, but as a pseudogene riddled with mutations and three stop codons.⁹¹ Our own version broke about 61 million years ago; the guinea pig's broke about 14 million years ago.⁹²

So a guinea pig fed only rabbit pellets or hamster mix, foods made for animals that produce their own vitamin C, can develop scurvy, just like a sailor on a long voyage. The first signs are a poor coat, poor wound healing, poor appetite and weight loss.⁹³

13. The Flip Side: What Animals Eat That We Can't

Sensitivity cuts both ways. Humans have our own blind spots.

Birds and chilli peppers. Capsaicin makes chillies burn by activating the pain receptor TRPV1. In 2002, David Julius and Sven-Eric Jordt showed that the chicken version of TRPV1 still responds to heat and acid but ignores capsaicin; they pinpointed the capsaicin-binding region that birds lack.⁹⁴ (Julius later shared the 2021 Nobel Prize in Physiology or Medicine for his work on temperature and touch receptors.) Ecologists had already shown in 2001 that capsaicin deters seed-destroying rodents like packrats and cactus mice, but not birds like the curve-billed thrasher, whose droppings deliver viable seeds.⁹⁵⁹⁶ The chilli's "poison" is aimed squarely at mammals: a plant's version of directed deterrence.

Koalas and eucalyptus. Eucalyptus leaves are toxic enough to kill most mammals. The koala genome, published in Nature Genetics in 2018, revealed two large expansions of the cytochrome P450 CYP2C family, 31 genes, highly active in the liver, plus an expanded repertoire of bitter-taste receptors to help pick the least toxic leaves.⁹⁷⁹⁸ The cost of such a demanding diet: koalas may spend up to 22 hours a day resting.⁹⁸

The koala and the cat are mirror images. One expanded its detox genes to specialise on toxic plants; the other lost them because it stopped eating plants at all.

14. The Five Rules Behind It All

1. The dose makes the poison, and body size changes the dose. A 5 kg dog that eats 50 g of chocolate gets about ten times the per-kilogram dose of a 50 kg adult eating the same bar.
2. Clearance speed matters as much as the molecule. Theobromine lingers about two to three times longer in dogs than in people, so doses stack up.
3. Diet writes the genome. Cats lost UGT1A6 and their sweet receptor because meat-only diets stopped rewarding them; koalas multiplied P450 genes to survive eucalyptus. What evolution doesn't use, it lets decay; what it needs, it copies.
4. Same molecule, different wiring. Xylitol is nearly inert to the human pancreas but a potent insulin trigger in dogs. Tartaric acid is a pleasant sourness for us but hard for a dog's kidneys to excrete. Capsaicin burns a mammal's tongue and doesn't register on a bird's.
5. Plumbing matters as much as chemistry. Rodents can't vomit, and a rabbit's gut runs on a delicate microbial ecosystem. An antibiotic that cures a human infection, or a sugary snack a child shrugs off, can tip that ecosystem into a fatal toxin factory.

"Natural", "healthy" and "safe" are not properties of a food but of a particular body meeting that food.

15. Quick Reference Table

Food	Main risk species	Toxic agent	Main damage	Rough danger threshold
Chocolate / cocoa	Dogs (cats too)	Theobromine, caffeine	Heart, nervous system	Signs ~20 mg/kg; seizures ~60 mg/kg
Grapes, raisins, tamarind, cream of tartar	Dogs	Tartaric acid (likely)	Kidneys	>1 grape per 4.5 kg body weight
Xylitol	Dogs	Xylitol	Blood sugar, liver	>0.1 g/kg (hypoglycaemia); >0.5 g/kg (liver)
Onion, garlic, chives, leek	Cats > dogs	Organosulphur oxidants	Red blood cells	Cats: < 1 tsp cooked onion reported
Acetaminophen (paracetamol)	Cats	NAPQI (metabolite)	Red blood cells, liver	Cats: signs from 10 mg/kg
Avocado	Pet birds, livestock	Persin	Heart, mammary glands	Small amounts can kill budgies
Macadamia nuts	Dogs only	Unknown	Muscles, nervous system	Signs ~2.4 g/kg
Raw yeast dough	Dogs	Ethanol, CO₂	Stomach, whole-body metabolism	Any amount is a concern
Hops	Dogs	Unknown	Body-temperature control	Any amount is an emergency
Salt / play dough	Dogs (all species)	Sodium	Brain	Signs 2–3 g/kg; lethal ~4 g/kg
Sugary, starchy snacks	Rabbits, guinea pigs, chinchillas	Clostridial toxins (from gut overgrowth)	Gut	Regular treats raise risk
Oral clindamycin, lincomycin, amoxicillin and similar	Rabbits, hamsters, guinea pigs, chinchillas	Clostridial toxins (gut flora disrupted)	Gut	Contraindicated by mouth
Diet lacking vitamin C	Guinea pigs (and humans)	Missing nutrient	Skin, joints, immunity	Needs vitamin C every day

Thresholds are rough guides from veterinary references, not safe limits. Individual animals vary widely.

16. What to Do If Your Pet Eats Something It Shouldn't

• Call a vet or animal poison hotline right away, even if your pet seems fine. In the US, the ASPCA Animal Poison Control Center is (888) 426-4435 (a fee may apply). Elsewhere, contact your local emergency vet.
• Don't wait for symptoms. Xylitol can act within an hour; grape and onion damage may not show for a day or several days; hops can kill within hours. For rabbits and rodents, which can't vomit, look for an exotics vet.
• Never give a pet leftover human medicine, especially antibiotics for a rabbit, hamster or guinea pig.
• Don't induce vomiting yourself unless a vet tells you to. Salt water, once a common home remedy, can itself cause salt poisoning.⁶²
• Bring the packaging. Ingredients, cocoa percentage and the amount eaten let the vet calculate the dose.
• Prevent it: keep handbags (gum, mints, medication) off the floor, put leftovers away, secure compost and brewing supplies, and don't share the dumplings.

This article is for general education and is not a substitute for veterinary advice.

Footnotes

1. ASPCA, "ASPCA Poison Control Reaches 5 Million Cases of Animal Exposures" (July 2025). https://www.aspca.org/about-us/press-releases/aspca-poison-control-reaches-5-million-cases-animal-exposures-hotline ↩

2. Merck Veterinary Manual, "Chocolate Toxicosis in Animals" (2024). https://www.merckvetmanual.com/toxicology/food-hazards/chocolate-toxicosis-in-animals ↩ ↩² ↩³ ↩⁴

3. "Studies on theobromine disposition in normal subjects," Clinical Pharmacology & Therapeutics (1978). https://pubmed.ncbi.nlm.nih.gov/627135/ ↩

4. dvm360, "Chocolate (Proceedings)." https://www.dvm360.com/view/chocolate-proceedings ↩ ↩²

5. Texas A&M Veterinary Medical Diagnostic Laboratory, "Possible chocolate poisoning in a dog" (2024). https://tvmdl.tamu.edu/case-studies/possible-chocolate-poisoning-in-a-dog ↩

6. "Chocolate poisoning," PubMed Central. https://pmc.ncbi.nlm.nih.gov/articles/PMC1215566 ↩ ↩²

7. ASPCA, "Chocolate intoxication," toxicology brief. https://www.aspcapro.org/sites/default/files/m-toxbrief_0201.pdf ↩ ↩²

8. ASPCA, veterinary technician toxicology brief on methylxanthines. https://www.aspcapro.org/sites/default/files/l-vettech_0301.pdf ↩

9. ASPCA, "The Wrath of Grapes." https://www.aspcapro.org/sites/default/files/grapes.pdf ↩

10. ASPCApro, "Make a Resolution to Keep Your Veterinary Pet Patients Safe This New Year's Eve" (2025). https://www.aspcapro.org/resource/make-resolution-keep-your-veterinary-pet-patients-safe-new-years-eve ↩ ↩²

11. "Acute Renal Failure in Dogs After the Ingestion of Grapes or Raisins: A Retrospective Evaluation of 43 Dogs (1992–2002)," Journal of Veterinary Internal Medicine (2005). https://onlinelibrary.wiley.com/doi/10.1111/j.1939-1676.2005.tb02744.x ↩ ↩²

12. Dijkman MA et al., "Incidence of Vitis fruit-induced clinical signs and acute kidney injury in dogs and cats," Journal of Small Animal Practice (2022). https://dspace.library.uu.nl/bitstream/handle/1874/421091/J_of_Small_Animal_Practice_2022_Dijkman_Incidence_of_Vitis_fruit_induced_clinical_signs_and_acute_kidney_injury_in.pdf ↩ ↩²

13. "Acute kidney injury in dogs following ingestion of cream of tartar and tamarinds and the connection to tartaric acid as the proposed toxic principle in grapes and raisins," J Vet Emerg Crit Care (2022). https://pubmed.ncbi.nlm.nih.gov/35869755/ ↩

14. ASPCApro, "Toxic Component in Grapes and Raisins Identified." https://www.aspcapro.org/resource/toxic-component-grapes-and-raisins-identified ↩

15. Wikipedia, "Grape toxicity in dogs" (with primary citations). https://en.wikipedia.org/wiki/Grape_toxicity_in_dogs ↩

16. Merck Veterinary Manual, "Grape, Raisin, and Tamarind Toxicosis in Dogs." https://www.merckvetmanual.com/toxicology/food-hazards/grape-raisin-and-tamarind-vitis-spp-tamarindus-spp-toxicosis-in-dogs ↩ ↩² ↩³ ↩⁴

17. U.S. FDA, "Paws Off! Xylitol is Toxic to Dogs." https://www.fda.gov/animal-veterinary/animal-health-literacy/paws-xylitol-toxic-dogs ↩

18. PetMD, "Xylitol Poisoning in Dogs" (2024). https://www.petmd.com/dog/poisoning/xylitol-poisoning-in-dogs ↩

19. "Acute Hepatic Failure in a Dog after Xylitol Ingestion," PubMed Central. https://pmc.ncbi.nlm.nih.gov/articles/PMC4880608 ↩

20. U.S. FDA, "Paws Off Xylitol; It's Dangerous for Dogs." https://www.fda.gov/consumers/consumer-updates/paws-xylitol-its-dangerous-dogs ↩

21. ASPCA / Veterinary Medicine, "New findings on the effects of xylitol ingestion in dogs." https://www.aspcapro.org/sites/default/files/ze-vetm0207f_095-100_.pdf ↩ ↩²

22. "Xylitol toxicity in dogs," Compendium (2010). https://pubmed.ncbi.nlm.nih.gov/20473849/ ↩

23. Pet Poison Helpline, "Xylitol in Products." https://www.petpoisonhelpline.com/uncategorized/theres-xylitol/ ↩ ↩²

24. Merck Veterinary Manual, "Xylitol Toxicosis in Dogs" (2024). https://www.merckvetmanual.com/toxicology/food-hazards/xylitol-toxicosis-in-dogs ↩ ↩²

25. "Acute hepatic failure and coagulopathy associated with xylitol ingestion in eight dogs," JAVMA (2006). https://avmajournals.avma.org/view/journals/javma/229/7/javma.229.7.1113.xml ↩

26. Cornell University College of Veterinary Medicine, "Xylitol toxicities." https://www.vet.cornell.edu/departments-centers-and-institutes/riney-canine-health-center/canine-health-topics/xylitol-toxicities ↩

27. dvm360, "A pungent poisoning: Onion toxicosis in a cat" (2015). https://www.dvm360.com/view/pungent-poisoning-onion-toxicosis-cat ↩

28. "Hematologic changes associated with the appearance of eccentrocytes after intragastric administration of garlic extract to dogs," American Journal of Veterinary Research (2000). https://avmajournals.avma.org/downloadpdf/journals/ajvr/61/11/ajvr.2000.61.1446.pdf ↩

29. "Induction of onion-induced haemolytic anaemia in dogs with sodium n-propylthiosulphate" (1998); and Hokkaido University study of sodium n-propylthiosulfate (1995). https://exa.ai/library/publication/16nkhl1xbq6 ; https://exa.ai/library/publication/wvjdzhcr9l1 ↩ ↩²

30. "Isolation and Identification of Sodium 2-Propenyl Thiosulfate from Boiled Garlic That Oxidizes Canine Erythrocytes" (2003). https://exa.ai/library/publication/4kln4hpdqmz ↩

31. dvm360, "Toxicology Brief: Allium species poisoning in dogs and cats" (2005). https://www.dvm360.com/view/toxicology-brief-allium-species-poisoning-dogs-and-cats ↩

32. Merck Veterinary Manual, "Garlic and Onion (Allium spp) Toxicosis in Animals" (2024). https://www.merckvetmanual.com/toxicology/food-hazards/garlic-and-onion-allium-spp-toxicosis-in-animals ↩ ↩² ↩³ ↩⁴

33. "Allium species poisoning in dogs and cats," Journal of Venomous Animals and Toxins including Tropical Diseases. https://www.scielo.br/j/jvatitd/a/HB5wqsgNcbhcg8cGm3hy95j/?lang=en ↩

34. "Household Food Items Toxic to Dogs and Cats," Frontiers in Veterinary Science, PubMed Central. https://pmc.ncbi.nlm.nih.gov/articles/PMC4801869/ ↩

35. Court MH & Greenblatt DJ, "Molecular genetic basis for deficient acetaminophen glucuronidation by cats: UGT1A6 is a pseudogene…," Pharmacogenetics (2000). https://europepmc.org/article/MED/10862526 ↩

36. "Evolution of a Major Drug Metabolizing Enzyme Defect in the Domestic Cat and Other Felidae: Phylogenetic Timing and the Role of Hypercarnivory," PLoS ONE (2011). https://pmc.ncbi.nlm.nih.gov/articles/PMC3065456/ ↩

37. VIN / WSAVA 2013, "Feline Therapeutics." https://www.vin.com/apputil/content/defaultadv1.aspx?id=5709852&pid=11372 ↩ ↩²

38. ASPCA, "Acetaminophen and Cats." https://www.aspcapro.org/sites/default/files/a-vettech_0103.pdf ↩

39. Li X et al., "Pseudogenization of a Sweet-Receptor Gene Accounts for Cats' Indifference toward Sugar," PLoS Genetics (2005). https://journals.plos.org/plosgenetics/article?id=10.1371%2Fjournal.pgen.0010003 ↩

40. "Genetics of sweet taste preferences," PubMed Central. https://pmc.ncbi.nlm.nih.gov/articles/PMC3130742 ↩

41. "Isolation and identification of a compound from avocado (Persea americana) leaves which causes necrosis of the acinar epithelium of the lactating mammary gland and the myocardium." https://pubmed.ncbi.nlm.nih.gov/8581318 ↩ ↩²

42. ASPCA, "The Scoop on Avocado and Your Pets." https://www.aspca.org/news/scoop-avocado-and-your-pets ↩

43. Merck Veterinary Manual, "Avocado (Persea spp) Toxicosis in Animals." https://www.merckvetmanual.com/toxicology/food-hazards/avocado-persea-spp-toxicosis-in-animals ↩ ↩²

44. Association of Avian Veterinarians, "Toxic Plant Series: The Avocado." https://www.aav.org/blogpost/1907684/455565/Toxic-Plant-Series-The-Avocado ↩ ↩²

45. "Avocado (Persea americana) intoxication in caged birds," JAVMA (1989). https://pubmed.ncbi.nlm.nih.gov/2914792/ ↩

46. "Cardiomyopathy in ostriches (Struthio camelus) due to avocado intoxication." https://pubmed.ncbi.nlm.nih.gov/7595917/ ↩

47. Agriculture Victoria, "Case study – avocado and domestic ducks don't mix" (May 2026). https://agriculture.vic.gov.au/about/media-centre/media-releases/2026-releases/case-study-avocado-and-domestic-ducks-dont-mix ↩

48. Massey University, Poisonous Plants of New Zealand, "Avocado." https://poisonousplants.massey.ac.nz/data/avocado/avocado.html ↩

49. Merck Veterinary Manual, "Macadamia Nut Toxicosis in Dogs" (2024). https://www.merckvetmanual.com/toxicology/food-hazards/macadamia-nut-toxicosis-in-dogs ↩ ↩²

50. ASPCA, "Macadamia nut toxicosis in dogs," toxicology brief (2002). https://www.aspcapro.org/sites/default/files/x-toxbrief_0402.pdf ↩

51. Hansen SR et al., "Weakness, tremors, and depression associated with macadamia nuts in dogs," Veterinary and Human Toxicology (2000). https://pubmed.ncbi.nlm.nih.gov/10670081/ ↩ ↩²

52. Côté E, Clinical Veterinary Advisor: Dogs and Cats, 4th ed., macadamia nut toxicosis entry. https://online.flipbuilder.com/ulbm/gwik/files/basic-html/page1228.html ↩

53. ASPCApro, "Bread Ingestion in Pets on the Rise." https://www.aspcapro.org/resource/bread-ingestion-pets ↩ ↩² ↩³ ↩⁴

54. Merck Veterinary Manual, "Bread Dough Toxicosis in Animals" (2024). https://www.merckvetmanual.com/toxicology/food-hazards/bread-dough-toxicosis-in-animals ↩ ↩² ↩³ ↩⁴

55. ASPCApro, "The Rising Danger of Hops Ingestion in Pets" (2017). https://www.aspcapro.org/resource/rising-danger-hops-ingestion-pets ↩ ↩²

56. Duncan KL, Hare WR, Buck WB, "Malignant hyperthermia-like reaction secondary to ingestion of hops in five dogs," JAVMA (1997). https://pubmed.ncbi.nlm.nih.gov/8977648/ ↩ ↩²

57. "Retrospective analysis of hops toxicosis in dogs (2002–2014): 71 cases," J Vet Emerg Crit Care (2022). https://pubmed.ncbi.nlm.nih.gov/34498796/ ↩

58. "A retrospective evaluation of hops ingestion in 177 dogs (2005–2018)," J Vet Emerg Crit Care (2023). https://onlinelibrary.wiley.com/doi/10.1111/vec.13282 ↩

59. Pet Poison Helpline, "Hops." https://www.petpoisonhelpline.com/poison/hops/ ↩

60. Merck Veterinary Manual, "Toxicoses in Animals From Human Dietary and Herbal Supplements" (hops section, 2024). https://www.merckvetmanual.com/toxicology/toxicoses-from-human-vitamins-minerals-and-dietary-supplements/toxicoses-in-animals-from-human-dietary-and-herbal-supplements ↩ ↩² ↩³

61. Veterinary Poisons Information Service, "Hops Toxicosis in dogs" (2022). https://www.vpisglobal.com/2022/01/07/hops-toxicosis-in-dogs/ ↩ ↩²

62. Merck Veterinary Manual, "Salt Toxicosis in Animals." https://www.merckvetmanual.com/toxicology/salt-toxicosis/salt-toxicosis-in-animals ↩ ↩² ↩³

63. Côté E, Clinical Veterinary Advisor: Dogs and Cats, 4th ed., salt toxicosis entry. https://online.flipbuilder.com/ulbm/gwik/files/basic-html/page1798.html ↩ ↩²

64. Pet Poison Helpline, "Play Dough (Homemade)." https://www.petpoisonhelpline.com/poison/homemade-play-dough/ ↩

65. Khanna C et al., "Fatal hypernatremia in a dog from salt ingestion" (1997). https://pubmed.ncbi.nlm.nih.gov/9111719 ↩

66. Merck Veterinary Manual (pet owner version), "Salt Poisoning" (2024). https://www.merckvetmanual.com/special-pet-topics/poisoning/salt-poisoning ↩

67. Kienzle E, "Carbohydrate metabolism of the cat. 4. Activity of maltase, isomaltase, sucrase and lactase in the gastrointestinal tract in relation to age and diet" (1993). https://onlinelibrary.wiley.com/doi/10.1111/j.1439-0396.1993.tb00310.x ↩

68. FOUR PAWS, "Milk Is Not Good for Cats." https://www.four-paws.org/our-stories/publications-guides/milk-is-not-good-for-cats ↩

69. VetAgro Sup Animal Welfare Chair, "Cats can drink cow's milk, TRUE or FALSE?" (2024). https://chaire-bea.vetagro-sup.fr/en/cats-can-drink-cows-milk-true-or-false ↩

70. The Conversation, "Can cats drink milk? Despite the stereotypes, it's actually a bad idea" (2025). https://theconversation.com/can-cats-drink-milk-despite-the-stereotypes-its-actually-a-bad-idea-255227 ↩

71. Horn CC et al., "Why Can't Rodents Vomit? A Comparative Behavioral, Anatomical, and Physiological Study," PLoS ONE (2013). https://journals.plos.org/plosone/article?id=10.1371%2Fjournal.pone.0060537 ↩

72. "Emesis in Rodents: Present or Absent? A Critical Review of the Evidence and Implications for the Use of Rodents in Biomedical Research" (2025). https://exa.ai/library/publication/yr77bxxp057 ↩

73. Merck Veterinary Manual, "Nutrition of Rabbits" (2021). https://www.merckvetmanual.com/exotic-and-laboratory-animals/rabbits/nutrition-of-rabbits ↩ ↩² ↩³

74. University of Illinois College of Veterinary Medicine, "Rabbit Gastrointestinal Stasis Syndrome" (2024). https://vetmed.illinois.edu/2024/06/04/rabbit-gi-stasis ↩ ↩² ↩³

75. Merck Veterinary Manual (pet owner version), "Disorders and Diseases of Rabbits" (2025). https://www.merckvetmanual.com/all-other-pets/rabbits/disorders-and-diseases-of-rabbits ↩

76. House Rabbit Society, "Digestibility in the Rabbit Diet" (2024). https://rabbit.org/health/digestibility-in-the-rabbit-diet ↩

77. Merck Veterinary Manual (pet owner version), "Illness of Rabbits" (2026). https://www.merckvetmanual.com/all-other-pets/rabbits/illness-of-rabbits ↩ ↩²

78. Merck Veterinary Manual, "Lincosamides Use in Animals" (2022). https://www.merckvetmanual.com/pharmacology/antibacterial-agents/lincosamides-use-in-animals ↩

79. DailyMed, CLINDA-GUARD Drops (clindamycin hydrochloride) veterinary label. https://dailymed.nlm.nih.gov/dailymed/fda/fdaDrugXsl.cfm?setid=62c83acf-476e-4b35-aadf-5992349849ea ↩

80. Merck Veterinary Manual, "Bacterial and Mycotic Diseases of Rabbits" (2024). https://www.merckvetmanual.com/exotic-and-laboratory-animals/rabbits/bacterial-and-mycotic-diseases-of-rabbits ↩

81. "Utilization of cholestyramine resin as a preventive treatment for antibiotic (clindamycin) induced enterotoxaemia in the rabbit," Laboratory Animals (1992). https://journals.sagepub.com/doi/10.1258/002367792780809039 ↩

82. "Clindamycin-associated colitis in hamsters: protection with vancomycin," Gastroenterology (1977), citing Small JD, "Fatal enterocolitis in hamsters given lincomycin hydrochloride" (1968). https://pubmed.ncbi.nlm.nih.gov/892381/ ↩

83. Merck Veterinary Manual, "Table: Plants and Foods That Are Harmful to Rabbits." https://www.merckvetmanual.com/multimedia/table/plants-and-foods-that-are-harmful-to-rabbits ↩

84. Merck Veterinary Manual (pet owner version), "Food Hazards." https://www.merckvetmanual.com/special-pet-topics/poisoning/food-hazards ↩

85. ASPCA, "Rabbit Pet Parents: Beware of These Common Pet Toxins!" (2024). https://www.aspca.org/news/rabbit-pet-parents-beware-these-common-pet-toxins ↩ ↩²

86. Aguirre LS et al., "Acute heart failure in rabbits by avocado leaf poisoning," Toxicon (2019). https://doi.org/10.1016/j.toxicon.2019.03.024 ↩

87. Patson CN & Sladky KK, "Sodium intoxication in a domestic rabbit," Journal of Exotic Pet Medicine (2020). https://doi.org/10.1053/j.jepm.2020.09.005 ↩

88. The Vet Desk, "10 Foods That Are Harmful to Rabbits: Vet-Reviewed Health Facts & FAQ" (2025). https://thevetdesk.com/pet-health-wellness/rabbits/foods-harmful-to-rabbits ↩

89. SpectrumCare, "Toxic Foods for Hamsters" (2026). https://spectrumcare.pet/small-mammals/hamsters/conditions/hamster-toxic-foods ↩

90. Burns JJ et al., "Missing Step in Man, Monkey and Guinea Pig required for the Biosynthesis of L-Ascorbic Acid," Nature (1957). https://www.nature.com/articles/180553a0 ↩

91. Nishikimi M, Kawai T, Yagi K, "Guinea pigs possess a highly mutated gene for L-gulono-gamma-lactone oxidase…," Journal of Biological Chemistry (1992). https://pubmed.ncbi.nlm.nih.gov/1400507 ↩

92. "Inactivation dates of the human and guinea pig vitamin C genes," Genetica (2010). https://link.springer.com/article/10.1007/s10709-010-9537-x ↩

93. PetMD, "Vitamin C Deficiency in Guinea Pigs" (2023). https://www.petmd.com/exotic/conditions/cardiovascular/c_ex_gp_vitamin_c_deficiency ↩

94. Jordt SE & Julius D, "Molecular Basis for Species-Specific Sensitivity to 'Hot' Chili Peppers," Cell (2002). https://www.cell.com/fulltext/S0092-8674(02)00637-2 ↩

95. Tewksbury JJ & Nabhan GP, "Seed dispersal. Directed deterrence by capsaicin in chilies," Nature (2001). https://europepmc.org/article/MED/11473305 ↩

96. "A single TRPV1 amino acid controls species sensitivity to capsaicin," Scientific Reports (2020). https://www.nature.com/articles/s41598-020-64584-2 ↩

97. Johnson RN et al., "Adaptation and conservation insights from the koala genome," Nature Genetics (2018). https://www.nature.com/articles/s41588-018-0153-5 ↩

98. Science, "A koala's diet would kill most mammals. Their genome reveals how they survive." https://www.science.org/content/article/koala-s-diet-would-kill-most-mammals-their-genome-reveals-how-they-survive ↩ ↩²