Facial expressions and predicting behavior.

Originally when I thought about my topic for this first essay I was leaning more towards researching facial expressions in terms of lying and guilt. I'm addicted to the show Lie to Me where the main character works with law enforcement to catch alleged criminals by detecting their lies through facial expressions. Then when I started researching facial expressions I began finding these theories about what facial expressions are really about. Perhaps they aren't connected to our emotions, but are used as a means of predicting and expressing future behavior. A smile could mean "it's okay to approach me, I'm friendly" or a scowl could mean "i'm warning you to stop." In fact a scowl might not be an expression of anger at all, but a defense mechanism. Someone could be feeling the emotion fear, but is showing aggression. For example, a dog who is fearful of a human may bare its teeth and snarl, showing aggressive behavior in order to deter the human. Does this make sense to anyone else? At first I thought it was bullocks, yes I just said bullocks, but after I started reading the research and finding more information it started to make a lot of sense. There are definitely some unexplained questions which I hope to find the answers to once I delve deeper.