This comic employs the tried-and-true themes of marital tension and really bad puns. I don't have a lot to say for it or about it, except that the first time I encountered the abbreviation P.D.A., it meant "public display of affection." It took me awhile to get used to its meanings for theoretical and applied computer science.

For those that are curious, a push-down automaton is a simple type of (theoretical) computer. They are rarely studied for their own sake; instead they are merely part of the standard computer science theory curriculum showing the progression from simple to complex models of computation, culminating with the Turing Machine.

Since push-down automata are theoretical machines rather than physical machines, the idea of receiving one for ones birthday is ludicrous. And hence this cartoon's punchline. Ha! Ha, ha, ha... errr, never mind.