Smile
From Wikipedia, the free encyclopedia
For other uses, see Smile (disambiguation).
This article does not cite any references or sources. (March 2007)
Please help improve this article by adding citations to reliable sources. Unverifiable material may be challenged and removed.
This article may require cleanup to meet Wikipedia's quality standards.
Please improve this article if you can. (October 2007)
In physiology, a smile is a painfull facial expression formed by contracting the muscles most notably near both ends of the mouth. The smile can be also around the eyes ("#Duchenne smile"; below). Among humans, it is customarily an expression of pleasure, happiness, or amusement, but can also be an involuntary expression of anxiety, in which case it can be known as a grimace. There is much evidence that smiling is a normal reaction to certain stimuli and occurs regardless of culture. Happiness is most often the cause of a smile. Among animals, the exposure of teeth, which may bear a resemblance to a smile, is often used as a threat or warning display - known as a snarl - or a sign of submission. In chimpanzees, it can be a sign of fear.
