In this helpful slideshow of body positions and movements, a former FBI counterintelligence agent discusses what you can learn about someone's feelings / thoughts by how observing their body language.
The most interesting nugget's at the end: the best indicator of mood is what we are doing with our feet. If we move or kick our feet upwards, we're feeling good. Same with our thumbs or other gestures which defy gravity such as pointing our thumbs up in in our hands.
Speaking of communication, here's the one secret necessary to resolve argument and conflict: ask a single clarifying question about what another person's view is about. That's it!