Don’t be afraid to laugh. Laugh not make you look like a fool or make your authority will go down if you have appropriate reasons. But you don’t laugh on your self or alone because you would be called crazy people. Laugh is useful for your body healthy, too.
We’ve long know that ability to laugh can help you decrease major illness and stress of life’s problem. But, what laughter is ? Laughter is the physiological response to humor. It consists of two parts -- a set of gestures and the production of a sound. When we laugh, the brain pressures us to conduct both activities simultaneously. Many parts of the body will be change, even the arm, leg and trunk muscles. No less then fifteen facial muscles contract and stimulation of major face muscle. 
In extreme circumstances, the tear ducts are activated, so that while the mouth is opening and closing and the struggle for oxygen intake continues, the face becomes moist and often red (or even purple). The noises of laughter range from sedate giggles to boisterous guffaws.
Now that we know what laughter is, let’s look at how it can be good for you. Basically, laughter acts as a safety valve that shuts off the flow of stress hormones and the fight-or-flight compounds that swing into action in our bodies when we experience stress, anger or hostility. These stress hormones suppress the immune system and raise blood pressure. When we're laughing, natural killer cells that destroy tumors and viruses.
Laugh as responses to humor may be differences by the age, experiences, and knowledge possesses. It’s make explains why sometimes your little sister or brother jokes does not make you laugh. By the way, laughing now before this one forbidden by government.
(references from : express.howstuffworks.com)
