While most people consider that laughter is one of the nature's great treatments for a whole range of mental and physical diseases, it is still a serious scientific subject that researchers are trying to figure out. "Laughter is social." says Robert R. Provine, author of the book "Laughter: A Scientific Investigation", who has been studying laughter for decades. "Almost all people laugh 'ha-ha-ha' basically the same way. Whether you speak Mandarin, French or English, everyone will understand laughter. There is a pattern generator  in our brain that produces this sound. Laughing is also a good way of communicating. Babies laugh long before they speak. No one teaches them how to laugh. They just do it. People may laugh at a prank  on April Fools' day. But surprisingly, only 10 to 15 percent of laughter is the result of someone making a joke. Laughter is mostly about social responses rather than reaction to a joke. Deaf people laugh without hearing and people on cell phones laugh without seeing, which shows that laughter isn't dependent on a single sense but on social interactions. And laughter is not just a human thing. Chimps tickle  each other and even laugh when another chimp pretends to tickle them. Jaak Panksepp studies rats that laugh when he tickles them. It turns out rats love to be tickled. They return again and again to the hands of researchers tickling them, Panksepp's video shows. By studying rats, scientists can figure out what's going on in the brain during laughter. It has been found that laughter in rats produces a chemical that acts as an antidepressant  and anxiety-reducer. Scientists think the same thing probably happens in humans, too. This would give doctors a new chemical target in the brain in their effort to develop drugs that fight depression and anxiety in people. Even so, laughter itself has not been proved to be the best medicine, experts said. "No study has shown that laughter produces a direct health benefit," Provine said, "largely because it's hard to separate laughter from just feeling good." Why does the writer say "laughter is mostly about social responses rather than reaction to a joke"?
because people can communicate with each other by laughing. because laughter is the same sound in all the human's languages. because laughter is considered a basic language all people can learn. because everyone can understand the meaning of the word laughter.