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.