Smile

Smile
For other uses, see Smile (disambiguation). An Iraqi girl smilesIn physiology, a smile is a facial expression formed by flexing muscles most notably near both ends of the mouth, but also around the eyes. Among humans, it is customarily an expression of pleasure or amusement, but can also be an involuntary expression of anxiety. There is much evidence that smiling is a normal reaction to certain stimuli and occurs regardless of culture. Many studies indicate that smiling is an innate reaction, as children blind from birth smile; however feral children generally do not smile, perhaps lending evidence to the contrary. Among animals, the exposure of teeth, which may bear a resemblance to a smile, are often used as a threat - known as a snarl - or a sign of submission.
Smiling not only changes a facial expression, but can also make the brain produce endorphins which reduces physical and emotional pain, and give a greater sense of well-being.