A polygraph test can be passed by manipulating the body's response to control questions. A participant's lies are only considered lies when they register a higher response than control questions. The results can therefore be manipulated in a participant's favor if the participant is able to elicit a higher response to control questions than the relevant questions of the examination.
Polygraphers score tests by comparing physiological responses, such as breathing and heart rate, to control questions with responses to relevant questions. The participant fails the test if the latter reactions are greater. One method of inducing a higher physiological response to the control questions is to place something sharp such as a thumbtack inside the shoe, where it is easily accessible to the foot. This gives the participant the opportunity to step down on the thumbtack during control questions to induce high physiological responses, but not relevant questions.
Some polygraphers combat this method by insisting that participants remove their shoes before testing takes place. In this instance, a participant can use another method, such as thinking emotional thoughts or attempting to solve difficult math problems in his head. The ease with which participants are able to beat polygraphs is one reason why many anti-lie-detector campaigns are in effect, notes LiveScience.