I'm sure the pause is something he rehearsed at some point, but I've watched a few of his Q&As where he's done it. If I recall, he was even doing it in the 90s (the Q&A I'm thinking of is the one where he picks up a chair and pretends to use it as a shield). So while I'm sure it was something he originally rehearsed, it undoubtedly just became a habit of his over time.