It is an expression of the inner feeling/the way one understand a thing/happiness/joy, over an incidence just happened or happened much earlier and may happen in the future. It is an involuntary physical reaction accompanied by unarticulated sounds. It is a response to a stimuli either external or internal. While laughing one can find the contraction of the diaphragm and other respiratory organs.
AN ELABORATE DISCUSSION:
A new born child, though cries first, it smiles too. It must be an outcome of internal comfort.
Children's smile or laughter are uncorrupted, spontaneous, NATURAL and most powerful in healing the wounds of the elderly.
As soon as they enter the school, they learn many varieties of smile and Laughter. They start bullying and make fun of others and enjoy the same. Some times teachers too join this fun!
Take the case of grown-ups. There are enormous number of meanings in their every laughter. Both constructive as well as destructive laughter is prevailing in the society. There is a 'saying' in the Tamil Language, that denotes that 'a lady's laughter is highly dangerous'. Very sad indeed. Laughter out of ARROGANCE is commonly seen irrespective of their sex. We can see the villains laugh in Cinema/tv Serials.
In the great epic Mahabharatha, Draupathi, wife of Pandavas laughs at Duriyodhana,when he was walking along the Palace constructed by Pandavas and it added fuel to the already burning fire in the heart of Duriyodhana.
In Ramayana, you can see Rama, having a smiling face and faced everything with the same expression. When he was said that Coronation was to be taken place the next day he showed a smile: when Keikeyi asked him to go to forest for 14 years, the very same expression of smile did not change, a balanced view described as स्थितप्रग्न्य in Sanskrit.
Matha Amrithanandamayi once in her speech, explained the significance of smile and how much contagious a smile is.
Sense of Humor is found even in Great Saints.
SMILE AND LAUGHER:
Smile is a soundless, a mild expression which can be possible without even showing our teeth. Laughter, on the other hand is accompanied by unarticulated sounds, sound varies from person to person, it even varies from gents and ladies. Both, smile and laughter can be poisonous too. A cunning smile is equally poisonous like an arrogant laughter.
Nature has blessed the Human with the ability of smile and laughter. It is for us to decide whether to use it constructively or destructively.
'Laugh in the times of difficulty'-says the great poet of Tamil - Thiruvalluvar.
Laughter clubs are there to laugh, but a healthy laughter alone can give a healing effect deep inside.
Laughter lubricates the inner organs, the heart and the lungs in particular. You can add laughter too to the various preventive measures you take for Heart Diseases.
A smile is a shawl to show-off in the society, to hide your sorrow, to act as if you are happy.
THERE ARE CERTAIN PEOPLE IN THE SOCIETY WHO CANNOT BE MADE LAUGH OR EVEN SMILE WITH THE HELP OF 'LAUGHING GAS'-NITROUS OXIDE!!!