The Null Device
According to psychological studies, common folk wisdom about spotting liars is little more than superstition. Liars do not habitually avert their gaze, touch their noses or fidget any more than truth tellers do. Which is not to say that there might not be patterns of behaviour suggestive of lying:
Fibbers tend to move their arms, hands, and fingers less and blink less than people telling the truth do, and liars' voices can become more tense or high-pitched. The extra effort needed to remember what they've already said and to keep their stories consistent may cause liars to restrain their movements and fill their speech with pauses. People shading the truth tend to make fewer speech errors than truth tellers do, and they rarely backtrack to fill in forgotten or incorrect details.
Liars may also feel fear and guilt or delight at fooling people. Such emotions can trigger a change in facial expression so brief that most observers never notice. Paul Ekman, a retired psychologist from the University of California, San Francisco, terms these split-second phenomena "microexpressions." He says these emotional clues are as important as gestures, voice, and speech patterns in uncovering deceitfulness.
Also, it emerges that most people are poor at identifying liars, scoring little better than chance. Though one study, which included a group of US Secret Service officials, showed that they were considerably better at detecting liars than the average person.