Faking a smile is hard. As well as the zygomatic major that lifts the corners of your lips, real amusement operates 16 other sets of muscles in the face. One of these sets – the orbiculares oculi that raise your cheeks and squeeze the skin around your eyes – is almost impossible to move voluntarily. But try faking it anyway; a study by psychologist Richard Wiseman found that a third of the time, people couldn’t tell if a smile was real or false.
Putting on a fake smile could make you happy for real. In 1988, German researchers found that people told to clench a pencil between their teeth (which pushes the mouth into a smiling shape) subsequently felt their mood improve, and laughed longer and harder at cartoons.
A 2010 US study examined pictures of 230 professional baseball players in a 1952 yearbook. The 10 percent of players with real smiles in their photos died on average five years later than those who faked it, and seven years later than those who did not smile at all.
A human fake smile, with no movement of the orbicularis oculi muscles, has more in common with a chimpanzee’s expression of fear and rage than anything cheerful. To look like a happy chimp, you’ll need to cover your top teeth with your top lip and push out your lower jaw.
Smiles are essential emotional cues to other people, and partial paralysis of the face is a social catastrophe for stroke victims. To allow a stroke victim to smile when needed, surgeons can realign one side of the mouth into a permanent smile, or even graft new nerves into facial muscles.