Penis is a competitive beast (BBC)
Scientists believe the shape of the penis may have evolved to help men remove the semen of love rivals during sex.
ペニスの亀頭は行為中に他のオスの精子を膣外に追い出すようにできているらしいよ。
Scientists believe the shape of the penis may have evolved to help men remove the semen of love rivals during sex.
ペニスの亀頭は行為中に他のオスの精子を膣外に追い出すようにできているらしいよ。