Thomas Ormerod’s team of security officers faced a seemingly impossible task. At airports across Europe, they were asked to interview passengers on their history and travel plans. Ormerod had planted a handful of people arriving at security with a false history, and a made-up future – and his team had to guess who they were. In fact, just one in 1000 of the people they interviewed would be deceiving them. Identifying the liar should have been about as easy as finding a needle in a haystack.