A Real Laugh

Here are some things I didn't know about human laughter until I read this Washington Post story by a laughter researcher:

• We've developed the ability to fake-laugh, but people can spot a fake 70 percent of the time. Still, fooling people 30 percent of the time is pretty good, considering...
  
• "a fake laugh is basically an imitation of a real laugh...produced with a slightly different set of vocal muscles controlled by a different part of our brain.... if you slow down a 'real' laugh about two and half times, the result is strangely animal-like. It sounds like an ape of some kind, and while it’s hard to identify, it definitely sounds like an animal. But when you slow down human speech, or a 'fake' laugh, it doesn’t sound like a nonhuman animal at all—it sounds like human speech slowed down."
  
• Laughter in humans probably evolved as part of our need to play while young. Laughing while play-fighting signals other people that we're playing, not really fighting, and therefore not dangerous. Other primates also make sounds akin to laughing while playing.
  
• "Laughter triggers the release of brain endorphins that make us feel good, and it reduces stress."

While the false positive rate for assessing fake laughter may be 30 percent, I'm willing to be the false negative rate is close to zero. That fact is not mentioned in the story, though.