Rascal and Valentine have been bonded for more than a month now. I have NEVER seen either of them mount and hump. Well this morning I walked in and Rascal was on top of Valentine humping her! They are both spayed and neutered. They've been together for a while it seems and nothing like this has gone on. They just started grooming each other not that long ago, but I am curious as to why now all of the sudden he started humping her?