This document discusses the different categories of facial expressions: sadness and agony, anger, surprise and fear, disgust and contempt, and happiness. For each category, it identifies the key facial muscle movements and positions that are involved in expressing that emotion. For example, sadness is recognized by glaring eyes, raised upper eyelids, and lowered and brought together eyebrows. Anger involves a tightly clenched jaw, thinning of lips, and possibly an exposed rectangular mouth shape. Surprise and fear raise the upper eyelids and eyebrows and can cause a dropped jaw.