Laughter

Laughter is an expression or appearance of merriment or amusement. Laughter is a sound that can be heard. It may ensue (as a physiological reaction) from jokes, tickling and other stimuli. Inhaling nitrous oxide can also induce laughter; other drugs, such as cannabis, can also induce episodes of strong laughter (though such citations may only lay credit to accounts such as Reefer Madness). Strong laughter can sometimes bring an onset of tears or even moderate muscular pain as a physical response to the act due to muscular atrophy. Laughter can also be a response to physical touch, such as tickling, or even to moderate pain such as pressure on the ulnar nerve ("funny bone").

Laughter is a part of human behaviour regulated by the brain. It helps humans clarify their intentions in social interaction and provides an emotional context to conversations. Laughter is used as a signal for being part of a group — it signals acceptance and positive interactions. Laughter is sometimes seemingly contagious, and the laughter of one person can itself provoke laughter from others. This may account in part for the popularity of laugh tracks in situation comedy television shows.