SMILE

A smile is a facial expression formed by flexing the muscles near both ends of the mouth.^[1] The smile can also be found around the eyes (See 'Duchenne smile' below). Among humans, it is customarily an expression denoting pleasure, happiness, or amusement, but can also be an involuntary expression of anxiety, in which case it is known as a grimace. Cross-cultural studies have shown that smiling is a means of communicating emotions throughout the world.^[2] But there are large difference between different cultures.^[3] A smile can also be spontaneous or artificial (when people feel obliged to smile). Happiness is most often the motivating 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 also be a sign of fear. The study of smiles is a part of gelotology, psychology, and linguistics, comprising various theories of affect, humor, and laughter

Smiling is at the root of who we are as human beings. In fact, it's the very first thing parents take pride in when they monitor their infant's development.

A baby, long before it even begins to communicate verbally and physically, feels the message of a smile instinctively and almost always responds in kind.

Rabbi Yisrael Salanter taught that the face of a person is considered public property and one should always smile at everyone. A sour face can damage the mood of others and we are never allowed to inflict damage to others. How much happier would the world be if we all smiled at each other?

This is exactly what Ethics of the Fathers (5:15) has in mind when it says "Accept all people with a pleasant face."