a fly on the wall
墻上的一只蒼蠅（表示想要偷聽或觀察別人而不被發現的愿望）
口語·表達想偷聽或觀察的愿望
英文釋義
To be an unnoticed observer; to be able to witness a situation without being noticed
例句
I wish I could be a fly on the wall during their secret meeting.
典故來源
源于蒼蠅常停在墻上不被注意，比喻暗中觀察而不被發現的狀態。