The BBC has a fun experiment where you're challenged to "Spot the Fake Smile" on 20 individuals. I didn't do much better than 50 percent. Good thing I don't play poker. The experiment is based on the amazing work of retired University of California psychology professor Paul Ekman, who spent a career studying emotion and facial expressions. Most famously, Ekman researched "microexpressions," subtle "tells" that reveal when someone is lying. He's the author of Telling Lies: Clues to Deceit in the Marketplace, Politics, and Marriage and Emotions Revealed, among other books, and the inspiration behind the TV drama Lie To Me.
"Spot the Fake Smile" (Thanks, Bob Pescovitz!)