before you can say knife

(informal)very quickly; almost instantaneously

(非正式)极快地，立刻

(that) one could cut with a knife

(of an accent or atmosphere) very obvious

（口音，气氛）非常明显的

get (或 stick) the knife into (或 in) someone

(informal)do something hostile or aggressive to someone

(非正式)加害某人，跟某人过不去

go (或 be) under the knife

(informal)have surgery

(非正式)做手术

the knives are out for someone

(informal)there is open hostility (towards someone)

(非正式)（对某人）剑拔弩张

like a hot knife through butter

very easily; without any resistance or difficulty

轻而易举；势如破竹

anti-aircraft fire would slice through the car like a hot knife through butter.

防空火力将轻而易举地把汽车打成碎片。

twist (或 turn) the knife (in the wound)

deliberately make someone's sufferings worse

故意让人更加痛苦，揭人疮疤

under the knife【非正式用语】

Undergoing surgery.

进行外科手术