按：这是Science of Us网站一则趣闻。下面的视频在Facebook已经被浏览了有近3000万次。这里仅把第一段翻译下来，视频和英文文字一并附后。 

  本月早些时候被上传到Facebook上的一段视频正在网上热传，浏览量已经超过2600万次（按：9月15日的数据），视频的主角是一位“狡猾”的宝宝。故事的基本情节是：每次当她爸爸给她剪手指甲时，她都喊叫着并做出一脸苦相，很快又化作咯咯的笑声，显然是为她和她的小玩笑而得意。

A devious infant is the protagonist of a recent viral video that was posted to Facebook earlier this month and has since racked up more than 26 million views. The basic plot line: Every time her dad goes to cut her fingernails, she cries out and makes a pained face — then quickly dissolves into baby giggles, clearly pleased with herself and her little joke.

宝宝何时会开玩笑.zip （“脸书”视频上传不成功，本文末最后链接不知可否打开？若不行，这里可以下载，仅1.7M）

She’s pranking him, in other words, and it’s a pretty good gag, too. And this brings us to an interesting question: At what age do babies start making jokes? I don't just mean funny faces or weird noises, but jokes — as in, the ability to set up and subvert an expectation? And what does that tell us about their psychological development? This is something that researchers are starting to study in earnest, and the scientific pursuit is something of an about-face from a once commonly held theory in the 20th century that babies only reacted to humor, but weren't able to crack a joke themselves.

When you think about it, a joke is a pretty complicated thing, especially for a human so tiny as our little prankster here. To joke around with someone you have to be able to imagine the world from their perspective; you have to be able to make a good guess, in other words, at what their reaction might be, so that you can upend it. "Teasing, therefore, involves playing in the realm of minds," write Vasudevi Reddy and Gina Mireault, co-authors of a recent paper on the subject.

Psychologists call this theory of mind, and it's something that starts developing in infancy. According to Reddy and Mireault's paper, babies will typically start this variety of teasing jokes by around 9 months of age, which suggests that by this age infants are able to do this perspective-shifting trick — something that may be one of the building blocks for the development of empathy. The baby girl in this video looks a little younger than 9 months (I think?), but she seems to be catching on to this joke thing just fine.

Science of Us 原网址：http://nymag.com/scienceofus/2015/09/when-do-babies-start-making-jokes.html