What foods can be dangerous to your canine companion? Chocolate, for one, the darker, the worse. Xylitol, an artificial sweetener, can cause liver damage and a life-threatening drop in blood sugar. Both grapes and raisins can cause kidney failure in dogs, with vomiting and increased thirst potential symptoms of poisoning. Onions and garlic can cause the destruction of red blood cells and lead to anemia. And even a small amount of alcohol can be life threatening.