I've written before about the need for single-panel cartoons to create situations that are inherently amusing, as there is rarely enough space for a set-up followed by a punchline. And while there is a nominal set-up and punchline joke in this Off the Mark, the writing's real value is that it makes the absurd situation clearer. The situation is funny, but the labeling the writing provides is, in this instance, necessary.
This cartoon also has the advantage of having a well-known set of characters to play off. Most single-panels have to make do without any established characterization, which makes it both more difficult and more important to create an amusing situation.