This is one of my favorites, too.
He did that s**t to other tackles last season, too, IIRC.
With those long arms of his, he can get to the tackle before they're expecting it, so they're still in a backpedal and are off balance.
As impressive as Aldon Smith is, I've seen Patrick Willis tossing aside guards who were coming forward
and then stuffing the ball carrier.
The 49ers front seven is just unreal.