The computer is reading your mind

Which is probably legal under the Patriot Act, come to think of it.

This is weird. It's simple: pick a two-digit number, add the digits together and subtract that fromm the original, then stare at a symbol on the screen. The computer even knows if you're lying. I tried deliberately staring at the wrong one, and it still knew which number I had picked.

Akubra tip to The Stranger Blog. There's an explanation in the comments there, but it kind of ruined it for me. It's freaky if you don't know how it's done.