How quickly this can happen depends on the length of time a person is breathing the gas and the amount of the gas he or she breathes in.

VOA: special.2010.02.02

I find that even ten minutes to start with or even five minutes to start with is like a completely legitimate time, time well spent, just breathing, even with eyes open, I think it's harder when with eyes open, maybe that's something you lead up to.

从十分钟开始,甚至是五分钟,这段时间合情合理，真正被利用了，只需呼吸，甚至可以睁开眼，睁着眼睛会增加难度，你也需要为之努力。

普林斯顿公开课 - 人性课程节选