外国人说汉语的时候，我们觉得他们的口音挺有意思，而因为他们能把那么难的因发出来而感到佩服，所以才会抿嘴而笑。

When foreign friends are speaking Chinese and we are smiling because maybe we think they have an interesting accent, or maybe we feel it amazing that they can pronounce those difficult sounds.

youdao

但难的是一种发自内心的笑。

But the difficulty is a laugh from the heart.

youdao

笑不难，难的是把握笑的标尺。

Laughter is not difficult, it is difficult to grasp the scale laughing.

youdao

So, laughter is kind of a puzzle.

所以笑是一个难解之谜。

耶鲁公开课 - 心理学导论课程节选