Imagine you're out for dinner with a group of friends. Someone tells a joke and gets one person laughing, which gets a second person laughing, and so on. Is catching laughter like catching a cold? It's very likely.
Provine, the laughter researcher, found in one experiment that nearly half of his 128 undergraduate students giggled on first response to a simulated laugh [source: Provine]. And they did this despite knowing the source to be an artificial laugh-simulator.
According to Provine, contagious laughter raises the possibility that humans have laugh detectors. In other words, people are made to respond with laughter on hearing laughter itself, much like the mystery of spreading a yawn [source: Provine].