 Donkey punch

Donkey punch is the sexual practice of inflicting blunt force trauma to the back of the head or lower back of the receiving partner during anal or vaginal sex as an attempt by the penetrating partner to induce involuntary tightening of internal or external anal sphincter muscles or vaginal passage of the receiving partner.According to Jeffrey Bahr of Medical College of Wisconsin, there is no reflex in humans that would cause such tensing in response to a blow on the head, although striking a partner on the back of the neck or head could cause severe, even lethal injury.