in knots

When animals mate, specifically canines--I'm actually not sure about felines--the penis enlarges during climax and remains enlarged to the point where he is literally stuck inside the female for as long as it the mating process goes on. This happens to ensure insemination, and the male can ejaculate several times before he is shrinks down small enough to unmount. This is used as a kink of sorts in hybrid / abo fanfictions.