Comment by Emydz. on The Origin of Species - Chapter 15 : official translation

Basically when he c*ms (a lot)  inside the omlega and tries to pull out the a**hole won't allow it to come out so they create a knot. Until the hole looses up then he can pull out but after that they only want to do it with the person the knotted with. Anyone else dont feel as good for them.... thats what my understanding of it. Also their pheromones mix during the knotting system creating a closer bond with each other