Nonverbal communication, the sending and receiving of communication through "wordless cues" - the stuff that tells the story you won't tell. It's actually a fascinating branch of communication study. According to some studies 65-93% of communication is nonverbal (1).
Nonverbal communication is something we sometimes struggle with on a personal level. James had often remarked early in the relationship that sometimes our face and tone did not math the words coming out of our mouth. While we are really good at reading nonverbal communication (sometimes scary good), it could probably be said that we're not good at controlling it. (A Face Full Of Emotion: A Journal Entry - http://just-call-me-frank.blogspot.com/2012/01/face-full-of-emotion-journal-entry.html) Nonverbal communication can reveal how you are feeling, even if it's not intentional.
(1) Burgoon, J.K. (1994). Nonverbal Signals. In M.L. Knapp & G.R. Miller (eds), Handbook of Interpersonal Communication. (p. 235). Newbury Park, CA: Sage.