Laughter is an audible expression or the appearance of happiness, or an inward feeling of joy (laughing on the inside). It may ensue (as a physiological reaction) from jokes, tickling or other stimuli. It is in most cases a very pleasant sensation.
Laughter is found among various animals, as well as in humans. Among the human species, it is a part of human behavior regulated by the brain, helping humans clarify their intentions in social interaction and providing an emotional context to conversations. Laughter is used as a signal for being part of a group — it signals acceptance and positive interactions with others. Laughter is sometimes seemingly contagious, and the laughter of one person can itself provoke laughter from others as a positive feedback. This may account in part for the popularity of laugh tracks insituation comedy television shows.
Laughter is anatomically caused by the epiglottis constricting the larynx. The study of humor and laughter, and its psychological and physiological effects on the human body, is called gel otology.