a fly on the wall
墙上的一只苍蝇（表示想要偷听或观察别人而不被发现的愿望）
口语·表达想偷听或观察的愿望
英文释义
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.
典故来源
源于苍蝇常停在墙上不被注意，比喻暗中观察而不被发现的状态。