Warning: this story is not for the squeamish. The most painful medical experience I've ever been through was an abscess on the tailbone, which suddenly happened when I was a sophomore in college. It begins feeling like a sore butt, then a sensation of pain when you sit down, and finally (after a couple of weeks) an inflammation that makes it almost impossible to move your knees toward your stomach without agony. My doc called it "Jeep riders' disease," which I thought was his personal joke, but then I discovered this really was the term army medics used to describe the problem. At some point the sufferer will notice that a red cyst is developing that can eventually become baseball-sized. Not only is it horribly painful, but it's embarrassing to take to the clinic: "Ugh, the area above my crack is swollen--help!" Turns out it's not actually caused by anything too personal, but by a genetic predisposition. The area where our precedessors used to grow a tail is suspectible to this ailment through a couple of possible causes: a tailbone which has a slightly misformed hollow at the end, or a problem with skin pores that leads to inflammation. Anyway, a few days of minor surgery takes care of the problem, but it shows you how evolution can still, literally, be a pain in the ass.
