A smile is a facial expression formed primarily by flexing the muscles at the sides of the mouth. It is believed it takes about 42 muscles to smile. Some smiles include a contraction of the muscles at the corner of the eyes, an action known as a "Duchenne smile". Smiles performed without the eye contraction may be perceived as insincere.
Among humans, smiling is an expression denoting pleasure, sociability, happiness, joy or amusement. It is distinct from a similar but usually involuntary expression of anxiety known as a grimace. Although cross -cultural studies have shown that smiling is a means of communication throughout the world, there are large differences among different cultures, with some using smiles to convey confusion or embarrassment.
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