My daughters and my dogs' tails have a close relationship. Sometimes that relationship is tested by a quick grab of a tail and sometimes tested by a swishing tail to the face. But no matter what, my dogs always wag their tails when we come home. That, of course, begs the question, "why do animals have tails?" SciShow Kids has the answer to that question in their latest video. The video explains how some animals use their tails to communicate and some use them for balance. The video also explains why humans don't need tails.