What exactly is a lie? Is it anything we say which we know is untrue? Or is it something more than that? For example, suppose a friend wants to borrow some money from you. You say "I wish I could help you but I'm short of money myself." In fact, you are not short of money but your friend is in the habit of not paying his debts and you don't want to hurt his feelings by reminding him of this. Is this really a lie?
    Professor Jereald Jellison of the University of Southern California has made a scientific study of lying. According to him, women are better liars than men, particularly when telling a "white lie," such as when a woman at a party tells another woman that she likes her dress when she really thinks it looks awful. However, this is only one side of the story. Other researchers say that men are more likely tell more serious lies, such as making a promise which they have no intention of fulfilling. This is the kind of lie politicians and businessmen are supposed to be particularly skilled at. the lie from which the liar hopes to profit or gain in some way.
    Research has also been done into the way people's behavior changes  in a number of small, apparently unimportant ways when they lie. It has been found that if they are sitting down at the time, they tend to move about in their chairs more than usual. To the trained observer they are saying "I wish I were somewhere else now." They also tend to touch certain parts of the face more often, in particular the nose. One explanation of this may be that lying causes a slight increase in blood pressure. The tip of the nose is very sensitive to such changes and the increased pressure makes it itch (痒).
    Another gesture which gives liars away is what the writer Demond Morris in his book <em>Manwatching</em> calls "the mouth cover". He says there are several typical forms of this, such as covering part of the mouth with the fingers, touching the upper-lip or putting a finger of the hand at one side of the mouth. Such a gesture can be interpreted as an unconscious attempt on the part of the liar to stop himself or herself from lying.
    Of course, such gestures as rubbing the nose or covering the mouth, or moving about in a chair cannot be taken as proof that the speaker is lying. They simply tend to occur more frequently in this situation. It is not one gesture alone that gives the liar away but a whole number of things, and, in particularly, the context in which the lie is told.  One sometimes tells one's friend a "white lie" because one wants to ______.