"Expression implies a revelation about the characteristics of a person, a message about something internal to the expresser."
I have noticed through homework exercises in my nonverbal communication class that we all share the same facial expressions, such as the seven universal expressions that Dr. Paul Ekman has identified. But I have also noticed that we as individuals add our own "twist" to that expression. Using myself as an example, I have very large teeth and usually find myself trying to cover them with my lips when I am displaying a "content" face. Because it is hard for me to make a content face, I have adjusted in some sort of way that shows what I am feeling but still allows me to me comfortable and confident in what expression I am displaying. Because my facial features want to leave my mouth slightly open when I am content, I have trained myself to be aware when this happens so I don't look like I'm lost in la-la land, daydreaming with my mouth open like perhaps a child would do. I also noticed a "tick" my husband does with his chin and that it underlying when he is making some emotional faces.
I like seeing unique things about people and their personalities so I'm sure I will be watching more and more when I see someone get emotional.