Alcohol – alcohol depresses a dog’s brain function and can cause a coma.
Coffee – the caffeine in a cup of coffee is a compound of methyxanthine that can increase a dog’s heart rate and cause seizures.
Macadamia nuts –just a few of these nuts can produce tremors, even temporary paralysis, in a dog’s hind legs. Experts have yet to determine why.
Garlic – garlic breaks down a dog’s red blood cells, leading to anemia and possible kidney failure from leaking hemoglobin.
Onions – the damage from onions to a dog’s hemoglobin is cumulative, so small tastes over time can be worse than wolfing down a whole bulb.
Grapes – grapes and raisins can cause renal failure in a dog. Toxicologists are still trying to learn why.
Chocolate – the chemical theobromine found in chocolate can be fatal to a dog. Just three ounces of dark chocolate or seven ounces of milk chocolate can bring on vomiting in a 50 lb. dog.
From National Geographic