So a scientist walks into a shopping mall to watch people laugh. There's no punchline. Laughter is a serious scientific subject, one that researchers are still trying to figure out.
Less than 20% of laughter is related to jokes; People are more likely to laugh in groups than when alone; Women laugh more often than men; Most laughter is in the context of regular conversation, rather than in attempts to stimulate laughs
Robert Provine says that homegrown laughter may be what ailing couples need most. Laughter is first and foremost a social signal that binds people together. It synchronizes the brains of speaker and listener so that they are emotionally attuned.