Do Not Feed to Dogs
Macadamia nuts: These Hawaiian nuts can cause fever, tremors, weakness and other unpleasant symptoms.
Avocado: They contain a chemical called persin, which is harmless to humans but can be toxic to dogs.
Do Not Feed to Cats
Tuna: ("What, no tuna?") Not only does tuna lack the nutrients cats need, but too much can lead to mercury poisoning.
Other raw fish: An enzyme called thiaminase, common in raw fish, destroys thiamine, also known as vitamin B1. This can lead to neurological disorders.
Alcohol: This is a no brainer, I think, but here's why no booze for our furry buddies: beer, wine and spirits act as a depressant on animals' nervous systems, potentially leading to breathing problems and even coma.
Animal Bones: Beef or chicken bones can damage your pet's teeth or splinter and cause damage in their digestive tract. Stick with treat bones made specifically for dogs and cats. (I use balance in regard to bones, using some ham bones or even shank bones that are very solid and have rounded edges.)
Chocolate or anything with caffeine: Foods like coffee and cocoa contain methylxanthines, which in high concentrations can cause heart palpitations, tremors, seizures, dehydration and death.
Grapes and raisins: Scientists aren't sure why, but eating these fruits can cause canine and feline kidney failure.
Gum, baked goods and candy: Many sweetened treats contain xylitol, which can cause liver failure.
Milk: Adult animals don't have the lactase to digest milk and feeding it to them can cause diarrhea.
Onions, garlic and chives: While these foods add flavor to human meals, they can cause red blood cell damage in pets. Cats are more at risk, but eating larger quantities can also make dogs sick. I'd heard about the onions but had in the past been told that a little garlic could be helpful in flea prevention,,,think I'll avoid the practice now that I've read this.