In 2007, one Jamie Langridge became $50,000 richer after winning intense national tournament in Las Vegas. Langridge beat his opponent decisively, with a classic open-hand technique. The sport? Rock-paper-scissors.

Such advanced games are possible because people don’t choose their hand shapes randomly. They are affected by moves that have gone before, and what other people are doing. Consider a new experiment by Richard Cook at University College London. Cook asked 45 people to face off against each other in several rounds of rock-paper-scissors, in exchange for real money. In every game, either one or both players were blindfolded.

Cook found that the players drew with each other more often when one of them could see (36.3% of the matches) than when