"These crimes know no borders. In Iran, children are forced into sexual slavery, involuntary servitude, while Iranian girls are trafficked into Pakistan and numerous other countries.

VOA: standard.2009.06.16

Laughter could be viewed as a form of involuntary noisemaking and it's contagious.

我们可以把笑声视为不由自主地发出的声音,然后笑声有感染性。

耶鲁公开课 - 心理学导论课程节选