In large enough amounts, chocolate and cocoa products can kill your dog. The toxic component of chocolate is theobromine. Humans easily metabolize theobromine, but dogs process it much more slowly, allowing it to build up to toxic levels in their system.
Derived from the roasted seeds of the cacao plant, certain properties in chocolate can be toxic to cats when they’re ingested, specifically, caffeine and theobromine. Eating these ingredients can lead to a number of medical complications—some of which may be serious—in your cat.