Scientific studies have consistently shown that it is extremely difficult to figure out who is telling the truth by watching or listening to the witnesses. The NY Times reports:
Like the rest of us, airport security screeners like to think they can read body language. The Transportation Security Administration has spent some $1 billion training thousands of “behavior detection officers” to look for facial expressions and other nonverbal clues that would identify terrorists.Sometimes a wife will show up in family court with some story of abuse, even tho the events are long past with no witnesses, objective evidence, police reports, medical treatment, or other corroboration. She wants increased financial support. There is no practical way of determining whether she is telling the truth or not.
But critics say there’s no evidence that these efforts have stopped a single terrorist or accomplished much beyond inconveniencing tens of thousands of passengers a year. The T.S.A. seems to have fallen for a classic form of self-deception: the belief that you can read liars’ minds by watching their bodies.
Most people think liars give themselves away by averting their eyes or making nervous gestures, and many law-enforcement officers have been trained to look for specific tics, like gazing upward in a certain manner. But in scientific experiments, people do a lousy job of spotting liars. Law-enforcement officers and other presumed experts are not consistently better at it than ordinary people even though they’re more confident in their abilities.
The TV show Lie To Me exaggerated and popularized the idea that psychological research has discovered people who can detect liars with 100% accuracy. If such abilities really existed, they would solve a lot of problems in court, TSA, and elsewhere. They do not exist.