under the 'knife 做手术

abc

knife 习惯用语
get your knife into sb; have (got) your knife in sb (informal)
■harm and continue to harm sb (usually not physically)whom you consider your enemy 对某人怀恨在心；屡屡伤害某人:
He’s had his knife into me for months, and every time I make a mistake, he tells my boss.
他几个月来都跟我过不去，每次我一犯错，他就告诉老板。

go under the 'knife (informal)
■have a medical operation 接受手术:
Peter hates his nose so much that he’s seriously considering going under the knife to have it made smaller.
彼得很不喜欢自己的鼻子，他甚至认真考虑要动手术弄小一点。

like a knife through 'butter
■(cut/go) through sth hard easily 轻而易举；毫无困难:
It went through the metal door like a knife through butter.
它毫无困难地穿过了金属门。

turn/twist the 'knife (in the wound)
■deliberately remind sb of sth they are already upset about, and so upset them even more 揭人疮疤；往伤口上撒盐:
After the divorce, her friend turned the knife in the wound by saying she had always thought that the marriage wouldn’t last.
离婚之后，她的朋友又雪上加霜，说她一直觉得这桩婚事不会长久。
All right. I know I was stupid. You don’t have to twist the knife.
好啦，我知道我很蠢，你就不必揭我的疮疤了。

■(you could) cut the atmosphere with a knife 另见cut

■not the sharpest knife in the drawer 另见sharpest