After two gay men have sex, sometimes one is impregnated through the anus. The name for a fetus passed through the anus is fecus. It's usually dead, but on a rare occasion, a live fecus may be born. A.K.A. Anal miscarraige.
Also see skleet, the verb of passing a fecus.
Dude, I was taking a shit, and bam! There was this bloody fecus in the toilet!