Two different toxins are in chocolate: caffeine and the alkaloid theobromine (lesser known and more dangerous). Ingesting chocolate can cause vomiting, diarrhea, depression, muscle tremors, excessive thirst with frequent urination. The dog can become agitated and start pacing. More dangerous symptoms can develop including elevated/irregular heart rate, blood pressure changes and seizures. Baking/cooking chocolate is the worst, and the younger or smaller the dog, the more dangerous (in large amounts even deadly) it is to them.