<P> Laughter is a physical reaction in humans and some other species of primate , consisting typically of rhythmical , often audible contractions of the diaphragm and other parts of the respiratory system . It is a response to certain external or internal stimuli . Laughter can arise from such activities as being tickled , or from humorous stories or thoughts . Most commonly , it is considered a visual expression of a number of positive emotional states , such as joy , mirth , happiness , relief , etc . On some occasions , however , it may be caused by contrary emotional states such as embarrassment , apology , or confusion such as nervous laughter or courtesy laugh . Age , gender , education , language , and culture are all factors as to whether a person will experience laughter in a given situation . </P>
where does laughter come from in the body
contractions of the diaphragm and other parts of the respiratory system