The offending chemical in chocolate is Theobromine. It is a cousin to caffine. The chocolates from worst to least is baking squares, semi sweet, dark, milk. White chocolate does not contain theobrimine. As I said, they would have to eat a whole bag or more to be fatal. Cats have the same reaction to the chemical as dogs. If a cat ripped open a whole box of bakers chocolate and ate the WHOLE thing, yes it's possible your cat would die. If any animal eats a little here and there, the most is an upset stomach.