Elijah has a few things like this that he's figured out. This one doesn't look as impressive here, but the first time he did it, he was only holding a washcloth. He could reach up and all the way back without letting go.
Don't watch this next one if you get queasy.
He's got a few more, like touching his thumb to his forearm (on the same arm, of course). These "tricks" make my wife cringe, which actually makes Elijah want to do them more.