A chemical reaction takes place inside the cat. Chocolate contains a chemical called theobromine which is toxic to cats and dogs. Unlike in humans, theobromine is not metabolised (broken down) by cats or dogs. This leads to a toxic build up of the chemical. This then leads to problems with the cat’s heart, bowels, nervous system and kidneys. The last step in the chain reaction is that the cat can have seizures, heart failure. Possible death may occur in the most severe cases.
Fortunately cats are not attracted to eating chocolate. So a person would have to force it on a cat. That would be cat abuse and probably a crime under animal welfare laws. A killing dose is approximately 100 to 200 milligrams per kilogram of body weight. Toxicity symptoms occur at much lower doses. For cats and dogs it is 20 milligrams per kg of body weight. Dogs are attracted to chocolate as they like sweet foods. Therefore it is a real danger to dogs.
IMPORTANT: I am concerned that cat haters may concoct the idea that they want to kill a cat with chocolate. Don’t. It’d be a crime and if you were caught the punishment in developed countries is not insubstantial. Plus you’d have a criminal record.
SOME PAGES ON TOXIC TO CATS: