Notice a sudden swallowing or an increased need to drink.
This is one of the nonverbal signals most difficult to simulate.
When someone decides to lie, their blinking frequency becomes significantly lower. Right after telling the lie, it noticeably increases.
Nervousness when lying is also reflected in the intensity of foot movements. Watch, therefore, how calmly your counterpart sits.
Liars often involuntarily rub their nose, cover their mouth or eyes.
When someone believes what they say, words and gestures are in harmony. If, however, words and gestures are contradictory, they are probably lying.
Liars' efforts to control their body language tend to cause other unnatural gestures. These include biting lips, rubbing hands, playing with jewellery or hair.
If you notice an expression - albeit fleeting - that does not match the spoken words, believe what you see and not what you hear.
After telling a lie, most liars immediately look downwards and away. Then they look at you again to see whether you believe them.
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Article source American Management Association - AMA official website