The Secret Service had never revealed how their agents were trained to pick up on these subtle facial cues.

"They're still learning to read each other's facial cues," Ms. Olsen-Harbich said.

To what extent they are picking up on facial cues, or bringing to bear their own prior familiarity with the social group, remains to be spelled out.

By identifying different facial cues, scientists are able to map them to their corresponding Action Unit code.

"Changes in estradiol predict within-women shifts in attraction to facial cues of men's testosterone".

You may not smile or frown, make eye contact, or use other facial cues that show how you feel.

While studying nonverbal communication, researchers noted that some subjects were able to read nonverbal facial cues before reinforcement occurred.

Chuck Jones commented on his ability to denote personality through facial cues.

"They learn to recognize facial cues that distinguish between real fighting and play-fighting."

However, human beings' brains are wired to be social, and facial cues like smiling are very important in communications.