There are quite a few things that your cat can’t eat and avocados are one of them. Avocados have something in them called Persin. Persin is a fungicidal toxin that can be very harmful to any kind of animal. Some avocados have more Persin in them than others. If your cats eat the pit, skin or leafs of the avocado, it can cause vomiting and diarrhea. Other affects are unknown so it’s a good idea to keep your cats away from them.