When the human nervous system comes under stress, it does not simply produce internal physiological changes and leave behavior unaffected. It drives a specific category of behaviors whose purpose is to reduce the internal arousal level and return the system to a calmer state. These behaviors are called pacifying behaviors, and they are among the most reliable stress indicators available to the skilled observer. They are reliable because they are not deliberate. Nobody decides to pacify. The behavior is driven by the autonomic nervous system’s self-regulation mechanism and produces physical actions that the person is usually entirely unaware of. The...