There are some strange parasite in form of a tail of a pokemon. They are like wormy and they are various kind of tails. Those seek human to attach and merge on the tailbone, the coccyx to can parasite the spine. It symbiose with the host as become his tail... however, the victim can't control his new tail. The tail link over the neuronal system as controlling feeling and thoughts. Rare case can give more features of the pokemon. The tail can get stronger and bigger by time and what human feed.