The current one, about SAT guessing, explains, basically, what looks like the one sense in which the SAT is a good test -- it's practically impossible to cheat.
The one before that, though, called "Relativistic Baseball," is awesome.
The question is, "What would happen if you tried to hit a baseball pitched at 90% the speed of light?"
And the answer is, basically, everyone dies.
Suppose you’re watching from a hilltop outside the city. The first thing you see is a blinding light, far outshining the sun. This gradually fades over the course of a few seconds, and a growing fireball rises into a mushroom cloud. Then, with a great roar, the blast wave arrives, tearing up trees and shredding houses.