long-division
Explanation
This comic takes the mathematical concept of long division and applies it to the human body in a darkly humorous way.
In the first panel, a child asks, "Do you know how long division works?" -- a standard math question. But the parent's answer is unexpected: "My arms? I know. Long. It's a tough problem and they will work on it, and maybe my brain will figure out a way to address the concern."
The comic then shifts to a darker register in the next panels: "Gradually over time, our bodies learn to do division, and we break down into smaller and smaller parts as we continue." This sounds like a description of cell division or even decomposition.
In the final two panels, someone says "Sure, you're an idiot" and "But ghosts don't degrade over time" -- implying that the conversation has been about death and bodily decay all along, and that ghosts (who don't have physical bodies) are the only ones exempt from "long division."
The pun works on multiple levels: "long division" is both a math operation and a description of the body's slow division/deterioration over a long period. The comic turns a simple homework question into an existential meditation on mortality, delivered with Weinersmith's characteristic deadpan.