Animals can’t talk, but they have other ways to express themselves. For example, when a dog is excited, he wags his tail. When he’s waiting for you to do something (like walk him), he’ll sit patiently and swing his tail back and forth while looking at you. At least, that’s what my Shih Tzu does when he’s asking for a walk.
Humans don’t have tails because we can communicate perfectly without them, and besides, we don’t really need them. You can buy them and wear them, but you can’t control them… Until now, that is.