Concern with crime and terrorism makes it increasingly important to be able to detect lying. Most lie detection tools used to date are arousal-based protocols. The majority of these protocols are based on the assumption that, because of their fear of being caught, liars will be more aroused when answering key relevant questions (‘Did you steal the money?’) than when answering comparison questions. According to the US National Research Council's well-documented report , however, this premise is theoretically weak. Liars do not necessarily reveal more signs of arousal when answering key questions. Conversely, truth tellers might be anxious and hence show signs of arousal when answering key questions.