Forced copulations are “pervasively common in many species of ducks,” writes Prum. These are socially organized “gang rapes” that are “violent, ugly, dangerous and even deadly” and even sometimes end in the death of the female.

But the females have mounted their own defense with an increasingly elaborate anatomy — including, in some cases, sharp turns in her reproductive canal that act almost as teeth, making it harder for ducks to inseminate during forced copulations.

‘Like a selection of sex toys from a vending machine in a strange alien bar, duck penises come in ribbed, ridged and even toothy varieties.’

“Male ducks had evolved penises that would enable them to force their way into an unwilling female’s vagina, and the females in turn had evolved a new way — an anatomical mechanism — to counter the action of the explosive corkscrew erections of male ducks and prevent the males from fertilizing their eggs by force,” writes Plum.