A lottery-show draw machine where you are the machine. Say digits from 1 to 9 aloud, as randomly as you can, and before each one the house seals its guess in an envelope; yours opens when you speak. A ticket at the end shows how far ahead of chance the predictor got, set against 206 people from a psychology study. Speech recognition runs in your browser, and typing works too.
Featured in: Theory you can poke at