Penis fencing

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For the human sexual behavior, see Frot.

Two flatworms of the species Pseudobiceros hancockanus penis fencing. The one on the left has inseminated the one on the right. The sperm (shown in white) is absorbed through pores on the skin, thus causing fertilization

Penis fencing is a mating behavior which certain flatworms, such as Pseudobiceros hancockanus, engage in. Species which engage in the practice are hermaphroditic, possessing both eggs and sperm-producing testes.

Child-bearing, while necessary for the continuation of a species, requires considerable resources from the mother. Thus, from a biological point of view, it is preferable to be the father rather than the mother.

The species "fence" using two-headed dagger-like penises which are pointed, and white in color. The "winner" is the organism that inseminates the other. The sperm is absorbed through pores in the skin, causing fertilization in the "loser".