“go under the knife”的意思可不是“在刀的下面走”，真实含义是接受手术；动手术。

【例句】
She said that she wants to look ten years younger, so she has decided to go under the knife.
她想使自己看起来年轻十岁，所以她决定做整容手术。

I have to go under the knife next week.
下周我得去做手术。