OK, this does not deserve a downvote. Come on. The scene, I actually don't know what it's from (I'll probably get down voted for that -- tho I DID live in the same neighborhood as Zach Galifiankis!), but yeah, looks like he's going thru math calculations in his head, so it's, in a sense a metaphor for, you know, either the words in your head that you cannot say, or like someone said, searching for words you can switch, or maybe just sort of the mental gymnastics of being a stutterer in a more general way. Plus the stress; the dude looks pretty stressed out.