Male ducks, whose genital organs are usually hidden from plain sight, have to erect them in such a way that they are able to tunnel through the labyrinth of the female ducks' vaginas.
The reason is that, while female ducks are not able to prevent the male ducks from ejaculating when inside their vaginal tract, they are able to limit how far the males can penetrate. And as such, selecting which male gets to fertilise the eggs within her.
Enough of description, watch the video and discover a new word...
COCKSCREW
