The idea that body language can help you figure out how a person really feels has been popularized and exemplified in the FOX TV show Lie to Me in which Dr. Lightman runs a company that specializes in determining whether people are lying or not through examining a person's body language and "micro-expressions".
Although this method is controversial and many people find it to be unreliable (as the show itself points out), our textbook points out, nonverbal leakage can be a very "powerful cue that we're trying to hide an emotion". There are however, several studies that provide evidence for micro-expressions revealing when a person is lying. For instance, work done by social psychologist Mark Frank at the University of Buffalo has identified conscious and unconscious cues that can suggest that someone is lying. His research is being used by investigative bodies around the world to detect these almost impossible to control micro-expressions.
Frank spent much time studying under the world's foremost expert in reading facial expressions, Paul Ekman, who conducted research that found many universal facial expressions that correlate to specific emotions. Each emotion is tied to specific movements of muscles within the face and they can be recognized across many cultures. So in a way, Mark Frank IS the real-life embodiment of Dr. Lightman. Of course it could be that Frank and his work were the inspiration for the character and show.
So next time you tell a lie, which statistically will be sometime VERY soon, you better hope who ever you're telling the lie to isn't a master at detecting micro-expressions.