2. Onions (and Garlic)
Onions, garlic and other foods in the Allium family, such as leeks and scallions, can all be extremely poisonous to dogs if consumed in sufficient quantity. "Onion and garlic poisoning results in oxidative damage to the red blood cells (making the red blood cells more likely to rupture) and gastroenteritis (e.g., nausea, oral irritation, drooling, abdominal pain, vomiting, diarrhea)," according to the Pet Poison Helpline. Garlic is also considered to be about five times as potent as onions, so think again before offering your dog some potatoes with the ingredient.