In fact, just because the world is round, you can already see if this is the Earth, to somebody that's the natural direction.

实际上,正由于地球是圆的,你们可以看到如果这是地球,对于某些人来说这才是惯常的方向

耶鲁公开课 - 基础物理课程节选

In some cases, the back of the head could be more expressive than the front, in which case this is your opportunity and I wish you luck.

有些时候,后脑勺确实比正脸更有表现力,这才是你们的机会,祝你们好运

耶鲁公开课 - 基础物理课程节选