The polygraph is used to detect deception on the assumption that when peo- ple lie, they become anxious and physiologically aroused in ways that can be measured. Here’s how the test is conducted. After convincing a suspect that the polygraph works and establishing his or her baseline level of arousal, the exam- iner asks a series of yes-or-no questions and compares how the suspect reacts to emotionally arousing crime-relevant questions (“Did you steal the money?”) and control questions that are arousing but not relevant to the crime (“Did you take anything that did not belong to you when you were younger?”). In theory, suspects who are innocent, whose denials are truthful, should be more aroused by the control questions; guilty suspects, whose denials are false, should be more aroused by the crime-relevant questions.