These two apparent males were jostling for position, I suppose, as I can't think of any other reason for the behaviour of the larger beetle pressing down on the small one and shifting its body around, presumably to dislodge it. It didn't seem to faze the little one, as he carried on to the end. The larger one eventually broke off, walked around as in a daze, then charged the smaller one, resulting in the photos of the small one hanging in the air. And folks say we have all the fun....