Ok, let's pretend that this is a sort of "second introduction" in which talk about the body language in extremely widespread.
I think now is a result of the fact that when we communicate with someone, send information not only with words but also through a variety of indirect signals which include gestures of the body, facial expressions and tone of voice.
All these "signals" are innate and therefore can not be controlled (for the most good we can hardly say I'm controllable!) And allow us to obtain a wealth of information on our party.
For our nature we tend to take advantage of them, but unfortunately the 'humanization' to which we were subject meant that, over time, started to give much weight to the words to the gestures.
Nevertheless studies in the 70s and 80s showed that the nonverbal component of a conversation between 65% and 80%. If we think about it, these figures are absolutely shocking, essentially does not matter what we say but how we say it.
Here, my goal is to make people pay more than minimum attention to all those subliminal messages that people send us, I assure you that deciphering the "language of the body is often possible to include conduct otherwise misunderstood.