Charlie Brown is known to remark, later on, "Why can't I have a normal dog like everyone else?" Such is his enthusiasm for the game of Fetch that he describes it out loud. Snoopy will have no part of it.
Impressing stick fetching upon the reader's mind in a form that sounds somewhat demeaning is essential to the joke. Phrasing it like that, and posing that exposition as Charlie Brown's excited words, that is not I'd call standard joke construction. Jokes have constructions you know, and there are fewer ways for putting them together than you might think. Finding a new way of building a gag is a difficult task. One of the aspects of Schulz's work I enjoy the most is his ability to so often to construct new kinds of gags. Many things about Peanuts seem to express a kind of genius, but to me this may be the greatest thing about it, Schulz's ability to present a joke to us in a clean, iconic way, that is understandable but not overstated. It is wonderful.
