Lie detectors are widely used in the United States to find out whether a person is telling the truth or not. Paleographers, the people who operate them, claim that they can establish guilt by detecting physiological changes that accompany emotional stress. The technique adopted is to ask leading questions such as:" Did you take the money?" or "Where did you hide the money?" and measure the subjects' electrical resistance in the palm or changes in his breathing and heart rate. Such a device has obtained widespread recognition. At first sight, it appears obvious that any simple, reliable method of proving guilty people is valuable, but recent research not only raises doubts about how lie detectors should be used but also makes it questionable whether they should be employed at all. The point is that, apart from many of the paleographers being unqualified, the tests themselves are by no means free from error, mainly because they ignore human imagination and creativity. Think of all those perfectly innocent people, with nothing to be afraid of, whose faces go red and hesitate in answering when a customs officer asks them if they have anything to declare. Fear, and a consequently increased response, may not be enough to establish guilt. It depends on whether the subject is afraid of being found out or afraid of being proved guilty. On the other hand, the person who is really guilty and whose past experience has prepared him for such tests can change the results by preparing the questions.