Last night, Jon Stewart used his favourite joke twice in one episode. It’s the joke where he coyly calls attention to the fact that a picture or prop on the show is not real. So first he pretended to write something and then called attention to the fact that the writing had clearly been done in advance by someone else (“I have a pen that writes like a marker!”) and then he made a joke after showing three fake comedy photos of himself (“apparently I always have the same outfit and expression”). I’ve lost count of how many times he’s done this joke, often with a capper line like “I don’t know why that is.” Other comedians use that kind of joke, of course, but Stewart uses it constantly, because it re-enforces his persona as the guy who’s on the side of the audience, and that includes joining them in nit-picking details. It allows him to play the part of the average guy, rather than the authority-figure host.