Alice+Andre-Clark

When you hear a funny joke （which we hope happens often）， something odd happens. The corners of your eyes crinkle1）. Your nostrils flare2）， and your lips pull back to show your teeth. Your breath comes out in short bursts， five times a second， while your voice makes "ha ha ha" sounds. You're laughing！

There are many kinds of laughs—belly laughs3） and chuckles4） and guffaws5） and giggles6） and nervous laughs and unkind laughs. Your laugh is distinctive， like your voice. But even though no two laughs sound exactly the same， we all know laughter when we hear it. Laughs in Kazakhstan are pretty much the same as laughs in Kentucky.

We usually don't decide to laugh. When you hear a good joke， you don't think， "Now I'll raise my lip and say 'hee-hee'." It happens automatically.

Babies laugh long before they can talk. And laughter is hard to fake. In experiments， people can tell a real laugh from a fake laugh two times out of three.

All this tells us that laughter is hardwired7） into our brains. But why do we do it？ And are we the only ones？

当你听到一则有趣的笑话时（我们希望这种事情经常发生），会发生一些奇妙的事情。你的眼角泛起皱纹，鼻孔张大，嘴向后咧开露出牙齿。你以每秒钟五次的频率急迫短促地向外呼气，并发出“哈哈哈”的声音。你笑了！

笑有很多种——开怀大笑、暗自窃笑、纵声狂笑、咯咯傻笑、紧张的笑和不怀好意的笑。和你的嗓音一样，你的笑声也是独特的。不过，尽管没有哪两种笑声听起来是完全相同的，但只要一听到声音我们就都知道那是笑声。哈萨克斯坦的人笑起来跟肯塔基的人笑起来几乎没有什么差别。

通常，笑不是由我们自主决定的。当你听到一个有趣的笑话时，你不会想着：“我现在要张开嘴说‘嘻嘻了。”你自然而然地就笑了。

婴儿早在会说话之前就会笑了。而且，笑很难伪装。在诸多实验中，人们都有三分之二的几率可以将真笑和假笑区分开来。

所有这些都告诉我们，笑是人类大脑固有的功能。但我们为什么会笑呢？我们是唯一会笑的生物吗？

The Laughing Zoo

If you tickle8） a rat， it will make a squealing9） sound so high-pitched10） that humans can't hear it （though other rats can）. Scientists are pretty sure that this is rat laughter. Rats like to spend time with other rats that laugh a lot， and with people who tickle them. Many social animals， from mice to chimpanzees and even penguins， make laugh-like squeals or pants11） when they're play-fighting or being tickled， and sometimes when they want to avoid a fight. Animals can't tell jokes， so what are they laughing at？ In animals， laughter is a way to tell others "It's OK！ This might look like fighting， but we're just playing！" That's an important message for social animals to share. In play fights they practice biting and chasing， which might seem threatening. But if everyone is laughing， it stays friendly.

For both people and animals， laughter feels good. When you laugh， your body relaxes and your brain releases chemicals that make you happy. This is your brain's way of saying， "That was great！ Do that again！" Your brain likes you to explore and take risks. But it also wants you to be OK. So when it senses a little fear followed by immediate relief， it says， Great！ And that triggers a laugh.

Humans are more complex than mice or chimpanzees， and so is our laughter. We still laugh at tickling and chasing， but we also laugh at jokes and puns12） and even clowns in funny shoes.

Just as we enjoy running and jumping to flex13） our muscles， hearing a joke is a fun way to flex our mental muscles. Jokes help us think creatively and see things in new ways. They also help us think better by making mistakes fun. That's important！ If you want to do great things， you have to be prepared to make a lot of mistakes and not let them get to14） you. Jokes give us lots of practice at being flexible， thinking in new ways and correcting ourselves quickly. And the brain rewards this mental play with laughter. It feels so good that we like to do it again and again. Tell me another joke！

Of course， jokes aren't the only things we laugh at. Some people laugh when they're nervous. It's a way of releasing tension， so we don't explode15）.

Laughter can sometimes have a dark side， such as when we laugh at other people's mistakes or accidents. This laughter is not always kind. Why do we do it？ Maybe because we're always a little bit worried about doing something wrong ourselves. When someone else goofs16）， it can be a relief—at least it wasn't me！

Practical jokes17） set up this kind of laugh. They put other people into situations where we can laugh at them， which can be tricky—if the person has a good sense of humor， he or she may be able to laugh at the joke along with you. But often practical jokes make people mad.

Surprisingly， most of the time when we laugh， it's not because someone made a joke or did anything silly. In fact， when researchers at the University of Maryland followed people around a mall and counted all their laughs， they discovered that most laughs happen in ordinary conversations. People laugh after saying things like， "I'll see you guys later" or "There you go！" But why？

These everyday laughs fill pauses and help people read each other. Even friendly chatting is full of small moments that could sound rude if you take them the wrong way—laughs keep everything friendly. People also laugh after saying something that might sound a bit odd or new or contrary. The laugh says， "I'm just playing with this idea， it's OK" or "I'm not mad". They help the conversation move along. Sometimes， laughter simply shares a happy mood. When you laugh it makes your friends laugh too. And laughing feels good. So go ahead and spread it around！

Laughing uses lots of muscles and fills your lungs with oxygen—it's actually quite good exercise. It relaxes your body and relieves stress. Being in a cheerful mood boosts your immune system， so you can fight off sickness more easily. Patients in hospitals even report that funny books and movies help them feel less pain—though when scientists tested this idea， they found that scary movies work just as well.

Laughter can even help you be brave. It is a potent18） weapon against fear and things that scare us. If you can laugh at the monsters under the bed instead of being paralyzed19） by fear， you'll have a big advantage. All together now： riddiculus20）！

And laughter can help you learn. You may have noticed that it's much easier to remember a funny story about George Washington than a list of battles he won. Humor gets you to pay attention and think， and rewards you with a good feeling. All that adds up to a stronger memory.

So laughter can make you happy healthy and smart—what are you waiting for？ Oh， a joke？

动物的笑

如果你胳肢一只老鼠，它会发出一种长而尖的叫声，声音尖到人耳都无法听到（但其他老鼠可以听到）。科学家们相当肯定这就是老鼠的笑声。老鼠喜欢跟其他爱笑的老鼠待在一起，也喜欢跟胳肢它们的人待在一起。从老鼠到黑猩猩，甚至包括企鹅在内的许多社会性动物在打闹、被胳肢或是有时想要避免打斗时，都会发出类似于笑声的尖叫声或喘息声。动物不会讲笑话，那么它们在笑什么呢？……