Joe Navarro was a body language expert for the FBI. His job was to catch spies. In this Wired video, he shares some tips. He also busts some myths. For instance, a lot of people think that crossed arms are a blocking behavior. Navarro says, "That's just nonsense."
Navarro has written a number of books about body language and interrogation techniques, including What Every Body Is Saying: An Ex-FBI Agent's Guide to Speed-Reading People.