We all know pi, at least the first three digits of it. If for some reason you forgot them though, there's good news. All you need to get that knowledge back is some aluminum foil, ingenuity, and a shotgun.
Calculating pi with a shotgun is far from efficient, but what it lacks in practicality it makes up for in awesomeness. And the shotgun-toting duo Vincent Dumoulin and Félix Thouin at the Université de Montréal in Canada have proven it, though unfortunately without video.
The premise is simple: Take a sheet of aluminum foil and draw a quarter circle on it, an arch reaching from corner to corner. Then fire a 28-inch barrel Mossberg 500 pump-action shotgun at it from about 60 feet away. Then do it again. Do it 200 times. After the carnage, you just count the number of holes inside the quarter circle and compare it to the number of holes outside. Multiply by 4 and you have pi. Or at least something close. Dumoulin and Touin got 3.131, a 0.33 percent deviation from the real thing.
As fun as it may be, the shotgun part is just flair. This kind of calculation is called the Monte Carlo method, and can be much more boringly executed by just sprinkling some grains of sand on the ground. Dumoulin and Thouin's excuse for the shotgun seems to be that in a post-apocolyptic world, 200 shotgun shells would be more readily available (and entirely wasteable?) than a fistful of sand. The rest of their science seems pretty solid, but that bit seems like kiiiiiind of a stretch. [The Physics arXiv Blog]