Arm Wrestle Yourself Help

[cmnervegna]

Theres this video by Julian Smith where he has a clip of him arm wrestling himself and its just amazingly done. I cant find any error or trace of how he accomplished this. Im kind of curious to see if maybe you guys can see anything or maybe you know how to get this effect done. Im mind blown.
Here is the link.
http://www.youtube.com/watch?v=6eLDgZ013sI&feature=related

Thanks guys.

 

[Cracker Funk]

It's pretty darn good, but it's not perfect. Not saying I could do any better (I can't), but you can definitely see that his hands don't line up perfectly, and there's a little movement that wouldn't happen if they were actually connected. To answer your question, looks like he's rotoscoping.