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

and it's contagious, you know.

很有感染力。

会打棒球吗？ - SpeakingMax英语口语达人

What do we know from research is that smiles are contagious.

研究证明笑有传染性。

哈佛公开课 - 幸福课课程节选

It's contagious, that is, it's transferred to other persons or objects, depending on how receptive they are--perhaps by physical touch, perhaps in the case of severe impurity by sharing an enclosed space, by being together under an overhanging roof, tent.

它会传染给另一个人，另一个物体，这取决于它们的接受度，也许是通过肢体接触，也许是因为呆在一个与世隔绝的空间里，同在一个屋檐下。

耶鲁公开课 - 旧约导论课程节选

Smiles are extremely contagious.

微笑极易蔓延。

耶鲁公开课 - 心理学导论课程节选

So smiles and laughters are contagious.

笑和笑声是传染的。

哈佛公开课 - 幸福课课程节选

Why? Because happiness is contagious.

为什么？因为快乐是感染的。

哈佛公开课 - 幸福课课程节选

So smiles are contagious.

笑是传染的。

哈佛公开课 - 幸福课课程节选

It's contagious.

笑是感染的。

哈佛公开课 - 幸福课课程节选