Facial expressions of happiness, fear, anger, and suffering can be reduced to the shapes of eyes and mouths. As suggested in [1, 2], the perceived emotions in facial expressions involve processing by the amygdala.
 R. Adolphs, D. Tranel, and A. Damasio, "The Human Amygdala in Social Judgment," Nature 393, 1998 pp. 470–474.
 P. Vuilleumier, "Staring Fear in the Face" Nature 433, 2005 pp. 22–23.