Pet play. Man has always thought they have some traits like a certain animal (of your choice). But when Woman points that very thing out, Man gets flustered beyond belief. Man wants to hear Woman say it again and again. Woman notices this and begins to experiment: calling Man a nickname that recalls that animal, getting them ears and/or a tail, petting them, talking to them like they’d talk to that animal. The play makes them both Man and Woman happy and excited. (Bonus points if your characters are already anthro and you write them wanting to play another animal!!)