They glide up on one another, kinda turn sideways, and twitch. Is this a threatening gesture or are they trying to mate or something? It's fun to watch and they really seem to be enjoying themselves. Whats going on, thanks.
Your clowns are establishing dominance. Usually, a clown will show that they are submissive by turning itself perpendicular to its mate's belly and jittering. This will help them to figure out who will be female (dominant) and who will be male (submissive). Eventually one of them will stop doing it to the other and only the submissive male will do it to the female.