You know, even some goes pass you on the street and you don't smile ostensibly you don't smile-- there are certain micro-muscles in your face that are moving that actually make you feel better.

即使路人与你擦身而过时，你没笑,表面上你没有笑-,但你面部的细微肌肉,会收缩，让你感觉更好。

哈佛公开课 - 幸福课课程节选