This is rather lengthy, sorry. The yelling contest starts around 2:40 (the first half is mostly Jim laughing at Noah making silly noises). I think my favorite thing in the world is how into it he gets while yelling. He stretches as tall as he can and bulges his little blue eyes out and just generally puts forth a damn fine effort.
I assure you that Noah is not, in fact, nekkid. He just has an unfortunate habit (which will probably be inherited by Jim, alas) of hanging around the house in his boxers.