Psychologist Paul Ekman has made a lifetime study of how people act when they lie. Usually they not only want the hearer to believe the words they are saying; they also want to cover up some strong emotion that they are feeling such as guilt, shame, fear, anger, pain, or even pleasure. By noticing the contradictions between their words and their behavior, Ekman found that he could catch them in the act of lying.

Ekman concludes that there are four kinds of behavior that can give a lie away: the liar's words, voice, body, and face. He says that liars try hardest to control their words and face, since they assume that that's what the listener will be paying attention to. Consequently "lie catchers" should also pay close attention to the speaker's voice and body signals, which he may forget to control.

Obviously most lies are untruthful words, and it's these words that we focus on. A common problem for liars is keeping their story straight. As we all know, one lie leads to another, and before the liar knows it, someone will comment, "But that's not what you said a few minutes ago." A less common but more fatal giveaway is what's called a "slip of the tongue," in which the liar accidentally tells the truth instead of the lie she intended to tell. Additionally, frequent pauses may indicate that she is making up the story as she goes along.

The liar's voice can also give her away, and the voice is much harder to control than the words. When telling a lie, she may speak unusually loudly or softly, may speed up or slow down her speech for no apparent reason. This can be because of the emotion she's hiding. The voice-clue that seems to be the most reliable is that when people are upset, their voices tend to become higher. But Ekman points out that vocal changes such as these are not always signs of lying; they simply indicate strong emotion which the person may be trying to conceal.

Somebody behaviors can be controlled, but others can't. When telling a lie, a person may swallow frequently, sweat, or breathe faster. Gestures can give her away: nervous gestures, such as swinging the foot, scratching or rubbing parts of the body, or twisting the hair often increase when a person is self-conscious or under stress. The normal gestures that usually accompany speech are often used less when someone is lying. Or the liar may accidentally use a gesture that contradicts her words, such as nodding "yes" while saying "no."

(А. П.МАРТИНЮК, І. О. СВЕРДЛОВА, І. Ю. НАБОКОВА АНГЛІЙСЬКА МОВА Збірник типових тестових завдань Навчальний посібник Київ — Харків «Веста» 2012)