Smile

In physiology, a smile is a facial expression formed by flexing the muscles most notably near both ends of the mouth. The smile can be also around the eyes. Among humans, it's 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. However, happiness is most often the cause of a smile (courtesy wikipedia).....................................................
But for me a smile is the most beautiful thing that humans can give... it lightens ur heart, brightens ur face, and its priceless...