Why can an FBI agent know so much about the criminal suspect sitting across the interrogation table? Is it just because of the polygraph machines they have? The answer is of course no. The "secret weapon" they have is the skill of deciphering body language. FBI agents often use facial expressions, gestures, body movements (behavioral psychology), social distance (spatial psychology), contact, posture, and even clothing to discover people's thoughts, intentions, honesty, etc.
