Smiles are controlled by two sets of muscles which are the zygomatic major muscles, that run down the side of the face to connect to the corners of the mouth, and the orbicularis oculi muscles that pull the eyes back. The orbicularis muscles are particularly important as they are used to cause what’s called “smiling eyes”. Smiling eyes, also called “crow’s feet”, where a classic wrinkling appears in the corner of the eyes is an indication of true happiness. The zygomatic muscles, on the other hand, are consciously controlled and are the ones that normally flex when we smile for the camera. Therefore, the appearance of crow’s feet is a great way of determining genuine enjoyment. Insincere smiles appear as exposed teeth and stretched lips across the face, with no wrinkles in the eyes. Crow’s feet however, can be faked with extreme smiles, as the full face ends up really squished-up. What separates the two is that in the real smile the corner of the eyes will turn downwards and the eyebrows will dip as well. The honest smile has also been called the “Duchenne smile”, after the French researcher Guillaume Duchenne who was first to research smiles.
Symmetry is important in true smiles. An honest smile will be even across both sides. Smiles that are not genuine are more pronounced on the left side of the face since they are consciously being controlled. Liars also find it difficult to smile, instead preferring a straight face, but when they do smile, it appears forced and especially strained showing their underlying stress. Smiling is a subconsciously submissive gesture and liars often worry about being caught so they feel that smiling might give them away. Therefore instead of appearing natural to the person they are lying to, they instead tense up and try to appear expressionless instead. Smiling can therefore be an effective way to come across as honest, although smiling too big, for too long, or at inappropriate times will have the reverse effect.