AvocadoSeems harmless, but the persin in avocado can be mildly toxic to cats and dogs--particularly smaller ones, who can experience heart congestion if they eat too much.
Onions, garlic, and chivesThese allium plants are especially dangerous for cats, and can cause anemia and red blood cell damage if consumed in excess. However, these plants are okay in small doses, so no need to worry about the minimal amounts sometimes used in pet foods.
Grapes and raisinsResearchers believe a mycotoxin in these fruits can cause liver damage and kidney failure in dogs, potentially resulting in a dramatic blood pressure spike and a coma.
Macadamia nutsToo many macadamia nuts can be inflammatory to dogs. They may suffer from swollen limbs and tremors, and eventually, weakened nervous and digestive systems.
Cooked bonesSince cooked bones become brittle, they can splinter and, when swallowed, potentially cause lacerations in the digestive system of dogs. The residual fat on cooked bones can also lead to pancreatitis.
Coffee and chocolateCoffee and cacao seeds both contain methylxanthines. When ingested by dogs or cats, this substance can cause symptoms of vomiting and diarrhea, panting, hyperactivity, abnormal heart rhythm, tremors, seizures, and can potentially lead to death. Dark chocolate, including baking chocolate, can cause the most severe symptoms -- it contains high levels of theobromine, which can damage a dog's heart and nervous system.
MilkThat classic image of a cat lapping up milk is false. Adult cats lack enough lactase, the enzyme that breaks down lactose, to properly digest milk. Drinking milk can cause digestive upset and diarrhea.
If you notice any possibility that your dog or cat has ingested any questionable foods or substances, call your veterinarian