There are many ways in which a person's body language can give you information about whether they are lying or not.
One of the biggest signs that a person is telling lies is that he avoids eye contact during conversation. He may also touch his face often, covering his mouth with his hand very often. Touching the nose is also said to be a sign of taking others' attention to cover up lies. A person who is not telling the truth may be trying to make you focus on his actions rather than his words.
When a liar (说谎者) tells lies, his physical expression is often very stiff (僵硬的). If he is smiling as he speaks, only the mouth will move. A real smile naturally causes movement of the mouth, eyes, forehead, cheeks, and jaw.
The liar's hand, leg and arm movements are toward his own body. He takes up little space. The person's body language is closed off. Liars do not look relaxed, even though they may be trying to give the impression that they are.
When explaining something, a liar usually feels uncomfortable with pauses (停顿) or silences. The person may speak gently or in disordered words. A very skillful liar is able to speak directly and with confidence. In fact, some salespeople are best at this skill.
If you doubt someone is lying, change the topic of conversation suddenly. The liar will willingly change topics with you and become more relaxed. A person who is telling the truth will generally become confused by this sudden change. Another sign of someone telling a lie is yawning (哈欠) — the person may try and look as relaxed as possible, and yawing and stretching are ways of achieving this.
