A smile is a facial expression formed by flexing the muscles near both ends of the mouth and by flexing muscles throughout the mouth. Some smiles include contraction of the muscles at the corner of the eyes (see 'Duchenne Smiling' below). Among humans, it is an expression denoting pleasure, sociability, happiness, or amusement, but can also be an involuntary expression of anxiety, in which case it is known as a grimace. Smiling is something that is understood by everyone despite culture, race, or religion; it is internationally known. Cross-cultural studies have shown that smiling is a means of communication throughout the world. But there are large differences between different cultures. A smile can also be spontaneous or artificial.