Practice with how much pressure needs to be put on the razor or if the thumb should hold hair against the razor's edge are each part of experimenting with this type of thinning out of hair.

这种方法需要反复练习，来摸准把头发按向刀刃的大拇指需要用多大力。

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The high-stress work often puts these airmen on the razor's edge between saving a life and losing their own.

CNN: Quade: Secretive military team allows reporter inside