2011-11-06
Explanation
This comic takes the well-known mathematical constant pi and literalizes its reputation for showing up unexpectedly in equations. In the first panel, a man is studying a paper and asks "Why is pi in this equation?!" His companion explains, "That'''s pi, dude. It pops up in all sorts of places that don'''t seem appropriate." This is a genuine mathematical observation -- pi appears in many formulas where you might not expect it, such as in probability theory (Buffon'''s needle problem), number theory, and various physics equations that have no obvious connection to circles.
The comic then takes this description literally. In the second panel, labeled "Later...", a giant anthropomorphic pi symbol has climbed into bed with the couple, cheerfully asking "Hey guys, whatcha doin'''?" The joke transforms the abstract mathematical concept of pi appearing in unexpected places into a physical character who literally shows up in inappropriate situations -- specifically, in their bed.
The votey panel adds a math pun as a punchline: one of the characters rationalizes pi'''s presence by saying "Wait, it makes sense. We were making a sine wave." This is a double entendre -- "sine wave" refers to the trigonometric function (which indeed involves pi), but "sine" sounds like "sign," and the undulating motion of a sine wave is being used as a suggestive reference to what the couple was doing in bed.