Grapes and raisins have often been used as treats for pets. But it’s not a good idea. Although it isn’t clear why, grapes and raisins can cause kidney failure in cats. And, a small amount can make a cat ill. Repeated vomiting and hyperactivity are early signs. Although some cats show no ill effects, it’s best not to give your cat any grapes and to keep grapes and raisins off countertops and other places accessible to your cat.