The cells of a girl's body, be that of her skin or fluids, if inserted into the male rectum, tend to cause a serious mutation on a man's intestine, which mutates into a bizarre, twisted form of womb. If the mutation goes further to the most drastic stages, all the inner lower organs and systems get affected, and that includes the scrotum, which, then, may have its sperm production corrupted. The semen might leak into your intestines, then! Therefore, do not EVER let yourself get pleasure in the ass, if you are a man! Otherwise, you may get pregnant and, if so, you'll be the father of your baby! I mean... the father AND the mother! Even if the girl just sticked her fingers... It's a scientific fact, guys!