before you can say knife
非常迅速地；立即；瞬间
口语·表示非常迅速
英文释义
very quickly or suddenly
例句
The thief snatched the purse and disappeared before you can say knife.
典故来源
源自19世纪英国俚语，'knife'发音短促，比喻动作快如刀光一闪。