Log rolling - what's this all about?

Could someone tell me what this is all about? Tristan loves to move things around by pawing at them and he'll do it almost obsessively. It's usually logs or long pieces of wood but he'll also do it with pvc pipe, square pieces of lumber or plastic, etc. He'll even do the pawing without an object. Please don't let it be something overtly sexual so that I'll die of embarrassment having put it on his blog. I don't think it is because it's all about pawing with both front feet at the same time. I think he might do it to show off but I can't really figure it out. Any insight?

Here he's having a fine old time. I made sure not to make any comments while recording. I'm usually cooing sweet things at him and sound incredibly goofy even to myself.