After reading the facial expression section in the textbook, I find out more about Ekman's research on facial expression of emotion. I read a chapter of facial expression of emotion that written by Dacher Keltner and Paul Ekman. As I dug out the chapter, I gradually found out that facial expressions are associated with some autonomic physiology. For example, the oblique eyebrows and concerned gaze of sympathy decreased heart rate and distressed facial expression increased heart rate (Eisenberg et al. 1989). And also, respiratory response of laughter was related to increasing heart rate (Ruch, 1993). Apart from those stuff, Ekman also talked about the accuracy in facial expression judgment. According to his paper, accuracy in facial expression judgment was quite high when people being judged were being truthful and poor when the people were lying. In this material, Ekman and Keltner also claim the cultural variation in facial expression. There are four points arguing cultural differences in facial expression. What makes me interested in is that actually, people from different culture have different inferences they draw from facial expressions of emotion. Here is an example that explains this point. U.S. as compared to Japanese college students were more likely to infer that an individual displaying a Duchenne smile was highly sociable (Matsumoto & Kudoh, 1993). Before studying this chapter, I never think about facial expression can convey this amount of information. It is interesting to "decipher" people's faces and know more about their mind! 
Reference-- http://www.paulekman.com/wp-content/uploads/2009/02/Facial-Expression-Of-Emotion1.pdf
This is interesting! I always think I can read people and how they are feeling by their facial expressions. I also wonder if facial expressions are learned, or if they are something we genetically know how to do. Interesting blog!