Penis fight, also referred as penis fencing, is basically a mating activity performed by certain species of flatworm, for example Pseudobiceros hancockanus. These flatworms are mainly hermaphrodites, i.e. a species not having a specific sex. Each individual flatworm features two penises which are white and pointed. Being hermaphrodites, each individual possesses both - ovaries to produce eggs and testes to produce sperms.
To perform the act of mating through penis fencing, each of the two flatworms attacks the other with its pair of sharp penises that feature the shape of a two-headed dagger. The process involves an aggressive battle during which both the flatworms try to pierce the other one's skin with one of their penises. The defeated one is inseminated by the winner organism, which moves away from the brutal one night stand scotch free. The skin of the loser organism absorbs the sperm through pores of skin, thereby resulting in fertilization and then child bearing.
The act of Penis Fencing is the strangest feature surrounding flatworms. Just because these are born as hermaphrodites that feature both male and female parts, certain genus of flatworms must get involved in an activity to decide on roles as male and female. The act of penis fencing is necessary for child bearing so as to continue with the species. However, the process demands a substantial amount of time and energy from both the organisms involved, more commonly the mother. None of the organism, therefore, desires to play the female part just for the reason that pregnancy is very strenuous on their body.