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There was a great article about this in The New Yorker, about a year or two ago. A group of people trained themselves to spot liars through careful attention to visual clues like subconscious facial muscle movement. The training worked; afterwards they could identify a liar at far better than chance.

The only problem? Having taught themselves to do this, they found they could never turn it off. They could tell when people were lying, even when they didn't want to know.