Laughter is an emotional release similar to crying, brought upon by a mild mental stress rather than an emotional stress. It happens when the mind has some notion of an expectation and then that expectation is replaced by something similar but different and unexpected.

         From sudden emotion created by humorous activities performed by others or by themselves.

         When they're happy and feeling good.

         Sometimes to prevent crying.

         Someone tickled them.

         It feels good to laugh.

         Laughter is good for our lungs as an outlet for some extra energy. We use 17 different muscles to smile and 43 different muscles to frown, so it's easier to smile than frown.

         Laughing also adds days to our lives. However, crying lessens our lives.

         Laughing could also be bad, because you might get bad luck.

Read more: http://wiki.answers.com/Q/Why_do_people_laugh#ixzz24lxz3ivW

Why do we laugh? The reasons we laugh, including "contagious" laughter, may be products of evolution. Natural laughter is a two-part, spontaneous, response to humor, that has physiological, psychological, and physical benefits. Most agree that we laugh when we find something to be humorous, yet different reasons exist for what we find to be humorous. Additionally, different things are humorous to us at different stages of life. Laughter, a physiological response to humor, can be broken down into two parts. The first is a set of gestures, and the second is the production of sound. The brain forces to conduct both responses simultaneously. From a physiological standpoint, a "sensor" in the brain responds to laughter by triggering other neural circuits in the brain, which, in turn, generate more laughter. Oddly enough, laughter is an orderly response, and almost occurs "spontaneously" during pauses at the end of phrases, earning it the name the punctuation effect. Human beings are the only species capable of laughter, and the average adult does so approximately 17 times per day. Good health is one of the many benefits of laughter. Laughter reduces our stress levels by reducing the level of stress hormones, and also helps us cope with serious illnesses. Physiologically, laughter promotes healing, by lowering the blood pressure, and by increasing the vascular blood flow and the oxygenation of the blood. Physical fitness stemming from laughter is a benefit known to few. Scientists estimate that laughing 100 times is equivalent to a 10-minute workout on a rowing machine, or to 15 minutes on a stationary exercise bike. The mere act of laughing exercises the diaphragm, as well as the abdominal, respiratory, facial, leg, and back muscles. Another benefit of laughter is that it improves our over-all mental health. Pent up negative emotions, such as anger, fear, and sadness, can cause biochemical changes in our bodies that can produce a harmful effect. Laughter provides a harmless outlet for these negative emotions, and provides a coping mechanism for dealing with difficult or stressful situations.

par·o·dy [par-uh-dee]  noun

1.

a humorous or satirical imitation of a serious piece of literature or writing: his hilarious parody of Hamlet's soliloquy.

2.

the genre of literary composition represented by such imitations.

sat·ire  sat-ahyuhr] noun

1.

the use of irony, sarcasm, ridicule, or the like, in exposing, denouncing, or deriding vice, folly, etc.

2.

a literary composition, in verse or prose, in which human folly and vice are held up to scorn, derision, or ridicule.

3.

a literary genre comprising such compositions.

bur·lesque  ber-lesk]  noun

1.

an artistic composition, especially literary or dramatic, that, for the sake of laughter, vulgarizes lofty material or treats ordinary material with mock dignity.

2.

any ludicrous parody or grotesque caricature.

3.

Also, bur·lesk . a humorous and provocative stage show featuring slapstick humor, comic skits, bawdy songs, striptease acts, and a scantily clad female chorus.

mock-he·ro·ic mok-hi-roh-ik] adjective

1.

imitating or burlesquing that which is heroic, as in manner, character, or action: mock-heroic dignity.

2.

of or pertaining to a form of satire in which trivial subjects, characters, and events are treated in the ceremonious manner and with the elevated language and elaborate devices characteristic of the heroic style.

lam·poon lam-poon] noun

1.

a sharp, often virulent satire directed against an individual or institution; a work of literature, art, or the like, ridiculing severely the character or behavior of a person, society, etc.

Why Do People Laugh?

Laughter is part of the universal human vocabulary. All members of the human species understand it. Unlike English or French or Swahili, we don’t have to learn to speak it. We’re born with the capacity to laugh.

One of the remarkable things about laughter is that it occurs unconsciously. You don’t decide to do it. While we can consciously inhibit it, we don’t consciously produce laughter. That’s why it’s very hard to laugh on command or to fake laughter. (Don’t take my word for it: Ask a friend to laugh on the spot.)

Laughter provides powerful, uncensored insights into our unconscious. It simply bubbles up from within us in certain situations.

Very little is known about the specific brain mechanisms responsible for laughter. But we do know that laughter is triggered by many sensations and thoughts, and that it activates many parts of the body.

When we laugh, we alter our facial expressions and make sounds. During exuberant laughter, the muscles of the arms, legs and trunk are involved. Laughter also requires modification in our pattern of breathing.

We also know that laughter is a message that we send to other people. We know this because we rarely laugh when we are alone (we laugh to ourselves even less than we talk to ourselves).

Laughter is social and contagious. We laugh at the sound of laughter itself. That’s why the Tickle Me Elmo doll is such a success — it makes us laugh and smile.

The first laughter appears at about 3.5 to 4 months of age, long before we’re able to speak. Laughter, like crying, is a way for a preverbal infant to interact with the mother and other caregivers.

An evolutionary perspective
We believe laughter evolved from the panting behavior of our ancient primate ancestors. Today, if we tickle chimps or gorillas, they don’t laugh “ha ha ha” but exhibit a panting sound. That’s the sound of ape laughter. And it’s the root of human laughter.

Apes laugh in conditions in which human laughter is produced, like tickle, rough and tumble play, and chasing games. Other animals produce vocalizations during play, but they are so different that it’s difficult to equate them with laughter. Rats, for example, produce high-pitch vocalizations during play and when tickled. But it’s very different in sound from human laughter.

When we laugh, we’re often communicating playful intent. So laughter has a bonding function within individuals in a group. It’s often positive, but it can be negative too. There’s a difference between “laughing with” and “laughing at.” People who laugh at others may be trying to force them to conform or casting them out of the group.

No one has actually counted how much people of different ages laugh, but young children probably laugh the most. At ages 5 and 6, we tend to see the most exuberant laughs. Adults laugh less than children, probably because they play less. And laughter is associated with play.

We have learned a lot about when and why we laugh, much of it counter-intuitive. Work now underway will tell us more about the brain mechanisms of laughter, how laughter has evolved and why we’re so susceptible to tickling — one of the most enigmatic of human behaviors.

Robert Provine, Ph.D., is a professor of psychology and neuroscience at the University of Maryland, Baltimore County. He is completing a book entitled “Laughter” that is scheduled to be published this fall by Little, Brown and Company.

Schadenfreude

Incongruity

Irony

Cognitive shift

A Brief and True Report of the New Found Land of Virginia, 1588

Thomas Harriot

They are a people clothed with loose mantles made of deer skins, and aprons of the same round about their middles, all else naked . . . having no edge tools or weapons of iron or steel to offend us.

If there fall out any wars between us and them, what their fight is likely to be, we having advantages against them in so many manner of ways, as by our discipline, our strange weapons and devises, especially Ordinance great and small, it may easily be imagined: by the experiences we have had in some places, the turning up of their heels . . . running away was their best defense

In respect of us, they are but a poor people, and for want of skill and judgment in the knowledge and use of things, do esteem trifles before things of greater value.

Most things they saw with us, as Mathematical instruments, sea Compasses, the virtue of the load-stone [magnet] in drawing iron, a perspective glass [telescope] whereby was showed many strange sights, burning glasses [magnifying glass], wild fireworks, guns, books, writing and reading, spring clocks that seem to go of themselves, and many other things we had that were so strange unto them, and so far exceeded their capacities to comprehend . . . that they thought they were the works of gods then men, or at leastwise they been given and taught us of gods.  Which made many of them to have such opinion of us, as that if they knew not the truth of God and Religion already, it was rather to be had from us whom God so specially loved, than from a people that were so simple.