I wanted to share the work of Paul Ekman, a psychologist who along with W.V. Friesen "developed the Facial Action Coding System in the 1970s by determining how the contraction of each facial muscle (singly and in combination with other muscles) changes the appearance of the face.
"They examined videotapes of facial behavior to identify the specific changes that occurred with muscular contractions and how best to differentiate one from another. They associated the appearance changes with the action of muscles that produced them by studying anatomy, reproducing the appearances, and palpating their faces. Their goal was to create a reliable means for skilled human scorers to determine the category or categories in which to fit each facial behavior." (These quotes are from the website for ordering the new version of this book, FACS .) Additionally, the Ekman site contains all manner of articles, photos, publications, and research tools.
Ekman has a new book out, called Emotions Revealed: Recognizing Faces And Feelings To Improve Communication And Emotional Life. Ekman describes how facial expressions work, purporting to differentiate between a fake and a real smile by mapping the muscle movements of both. He is a fascinating interview, and a recent interview appears on Terri Gross's Fresh Air .
It seems the information researched by Ekman, et. al. should be of interest and use to many magicians and mentalists.