People have learned to identify the emotions of their pets by indirect signs. If a dog wags its tail, for instance, it means that it’s happy. This is practically the same thing as a human smile. If a cat arches its back and rubs against your legs, it means that it wants to be pet, and, of course, be given a treat. But some animals are so skilled at using their facial expressions that you don’t have to guess what’s on their mind.