Obama's ease and Hillary's nervous laugh.

How much can we read from this little exchange? I love the way he pauses, giving her a chance to cackle (as if to say "gotcha"). After he utters his witticism, it's plain that the pause worked as comic timing. He used the pause to word the witticism perfectly, thus creating this delectable YouTube clip, which ends with more of that laughing of hers. Now, she's both laughing at his joke, which was a joke at her expense, and sounding nervous when he's being especially cool.