In the late 1960s, Paul Ekman--then a young psychology professor at the University of California, San Francisco, School of Medicine and just commencing his life's work--filled a San Francisco Victorian with a library of films showing 40 psychiatric patients' faces as they were interviewed. Ekman, who is now a leading figure in his profession, wanted to know whether he could isolate facial expressions to help diagnose mental disorders. A woman named Mary, who had attempted suicide three times before, smiled and spoke cheerily on her tape. As it happened, she was angling for a weekend pass--so that she could go home and kill herself.

"Mary was how I first discovered microexpressions," Ekman told me when I caught up with him on the set of Lie to Me, the Fox television drama inspired by his decades of research into how facial expressions, gestures, and other nonverbal behaviors reveal our emotions and--most pertinently--our deceptions. "Some young psychiatrists I was teaching asked whether I could help identify when a suicidal patient was telling the truth or lying about improving," he said. "Some of their patients had left the hospital and killed themselves within an hour. Mary, however, had confessed before she left that she'd been lying during a [previous] interview I'd filmed. Looking at the film, I couldn't see any evidence. So I went through it frame by frame for a week, and these microexpressions showed up--two instances, each a 25th of a second, out of 12 minutes."