Which expression do you think shows real pain? Attempts to fake expressions of pain typically involve the same facial muscles that are contracted during real pain. There is no telltale facial muscle whose presence or absence would indicate real or faked pain. The difference is in the dynamics. Human observers are at chance for telling them apart. The machine learning and computer vision system described by Bartlett et al. detects faked pain significantly better than humans. The system detects distinctive dynamic features of expression missed by humans. Spontaneous and deliberate facial movement is controlled by distinct motor pathways that differ in their dynamics. By revealing the dynamics of facial action through machine vision systems, the approach in Bartlett et al has the potential to elucidate behavioral fingerprints of neural control systems involved in emotional signaling. The real expression of pain is image B on the right.