Body language is part of the studies done in psychology and behavioural disciplines.
It is the unconscious response of a person. Much as the verbal communication is important, the often unnoticed portion which is our body response,are even more important.
For example, a person can nod his head in agreement but at the same time clutch his hand tightly and his hand muscles are stiffed. This body language reveals a contradictory messages.
Which one would you think is the real thought in the person’s head?
The body response are often more accurate depiction of a person’s thought.