Gladwell devotes much of Blink to our ability to quickly size up an emotional encounter through its human dynamics—facial expression, body posture, tone of voice, etc. Emotion is a subconscious thermostat-like arousal system that alerts us to potential dangers and opportunities, and attention is a focusing system that separates an emotionally significant foreground from its less significant background. Every person we meet is a potential danger or opportunity, so we must rapidly and subconsciously extrapolate subtle bits of body language into a comprehensive perception of intent. Our inner emotions have an automatic correlate in our external facial expressions and body language because it's important to our social species' welfare that we correctly perceive each other's intentions.

Gladwell doesn't discuss the recent significant discovery of mirror neurons, a class of neurons that seems to explain this cognitive phenomenon. Mirror neurons activate when we engage in goal directed behavior—but also when we perceive someone else engaged in that behavior. Examples include an infant's tendency to mimic facial expressions, and our tendency to yawn when we see someone else yawn. We commonly call it reading someone else's mind. Autistic people apparently have mirror neuron deficiencies and so are unable to sense what others are thinking. For a more complete discussion of mirror neurons, see my August 2002 column.

As indicated above, the quick extrapolation of an observed thin slice of a person into the entire person can lead to faulty judgment if the thin slice contains elements (such as skin color, gender, and body piercing) that inappropriately bias the judgment. Gladwell recounts how female and minority musicians were rarely hired by symphony orchestras before orchestras instituted a policy of using a screen to shield auditioning candidates from the selection committee.

Companies use brand logos and celebrity endorsements to deliberately bias the snap product judgments we make when shopping. Politicians use loaded terms to glorify themselves and demonize their opponent. We allow mass media to do our reflective thinking for us, to provide justification for the snap judgments we had made about the issue.