A volunteer deals cards from an ordinary deck into two piles, stopping whenever he likes. He tosses aside one of the piles and peeks at the top card of the other pile. Then he drops the remainder of the cards on top of this pile and deals everything again into two piles. The magician, who has never touched the cards, now divines which of the two piles contains the memorized card and indeed discovers the card itself.

This trick is based on the Penelope principle, a mathematical idea worked out by Scottish magician and computer programmer Alex Elmsley. Elmsley’s technique required a perfect faro shuffle, so David Rutter revised it into a simpler version that’s entirely self-working. It was presented at the 15th Gathering for Gardner conference last year.