A death erection (also named “angel lust”) is a postmortem erection happening when the man dies vertically or face-down and the corpse remains so.
When the body is dead, the smooth muscles of the arteries relax (die). In the dead body gravitation acts on the blood causing it to accumulate at the lowest point of the body. In a face down body, the blood enters the dead penis through gravity, causing an erection. The body must stay in that position to maintain the death erection until the blood clots.
Death erection can also be provoked by a traumatic death, especially asphyxiation (like in strangulation or hanging) accompanying the final spasms of the nervous system, and in this case ejaculation may take place. Some link this to brain or spinal cord injuries caused by the noose, as priapism (a persistent and painful erection) in living men has been associated with such conditions. Other rapid or violent deaths can also cause angel lust: bullet wounds to the brain or large blood vessels or poisoning.
In war time, death erection made an excellent war trophy, a method of humiliating the enemy by displaying the organ. Hanged women too can present a corespondent to this, translated trough engorged labia and vaginal discharges.