“For years psychologists have thought that a real smile, which reflects felt, positive emotion, is signalled by upturned lips and crinkly eyes. This genuine smile is named after the French physician Duchenne, who passed electrical currents through live subjects and took photos of their weirdly contorted faces.

Oddly enough when some people try to fake a smile they look like one of Duchenne’s subjects: in pain. It has been suggested that 80% of us are unable to conjure up a fake smile that will trick others because we don’t have voluntary control over the muscles around our eyes which signal the Duchenne smile.

Others, though, may well be much better at faking a real smile, which is a handy trick because people automatically trust, like and want to be with those who appear to be showing real emotion.

Writing in a recent issue of the journal Emotion, however, Krumhuber and Manstead (2009) question whether this 80% estimate is anywhere near the mark. In the first of a series of experiments they found that 83% of the people in their study could produce fake smiles that others mistook for the real thing in photographs.”

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