Direct dialogue (characters speaking to each other) is a minor form of communication. In real life body language communicates far more information about both the speaker and the listener than mere words. Research states that between 60 to 90% of communication is through body language not words. Body language consists of posture, movements or positioning of various parts of the body (head, arms, hands, torso, legs), gestures, mannerisms, facial expressions, eye movements, and eye contact or lack of eye contact. Through physical behavior humans communicate emotions, beliefs, opinions, hopes and intentions.
Mystery writers need to write story characters who behave in the same way. Showing character communication through body language is far more effective than telling about a character. Authors should review research about body language and incorporate the findings into their novels. Checkout this web site: Using Body Language.