He’s more vocal than usual

OK, so this isn’t a silent sign, but it’s noteworthy when your cat is more vocal than his usual quiet self. In fact, if it goes on for more than 24 to 36 hours, his meowing is a sign he could be sick. ‘Vocalization is a very broad clinical sign in cats—it can convey pain, but it can also convey many different underlying diseases,’ says Dr. Rossman. Despite popular opinion, purring doesn’t always mean he’s healthy and content.