There's already been at least one other crossover between Jeff Mallett's Frazz and Stephen Pastis' Pearls Before Swine (see Pearls Before Frazz). This one's a little different, though. The humor work whether or not you're familiar with Pastis' strip. But it works even better if you are. (click image to enlarge)
The strip carefully constructs an elaborate pun, panel by panel, and unleashes it on the unsuspecting reader. If you're familiar with Pastis' strip, then you recognize this as part of his repertoire. Pastis often does such puns, much to the annoyance of the strip's characters.
So Mallett not only references Pearls to build the joke, but also present a Pearl-like joke in the process. Humor that works on multiple levels. I love it.
(not sure why all the dialogue's typeset, though)