Happy tail syndrome is also known as kennel tail, splitting tail and bleeding tail. When a dog is excited and wags his tail rapidly he can injure it by hitting it against a hard surface like a table leg or wall. A dog can hit his tail hard enough on a hard surface that it causes a small cut or split on the tip of his tail. The cut tends to bleed a lot and as they continues to wag their tail, blood is splattered around the area.
Due to the cut being on the tip of his tail, it doesn’t heal quickly, it can be hard to stop the bleeding, and it can be recurring if the dog wags his tail repeatedly against a hard surface. Infection is a concern; in a worst case scenario, a portion of the tail may be amputated.