The human face is the most complex emotional signaling system in the animal kingdom. Over 40 distinct muscles, more than any other species, produce a range of expressions so fine-grained that trained observers can distinguish thousands of unique configurations. The face is where people direct almost all their social attention, where first impressions are formed, where trust and distrust are communicated, and where emotional states are both revealed and concealed. It is simultaneously the most watched and the most actively managed part of the human body. This creates a fundamental paradox. The face is where people look for truth, and...