be a fly on the wallto be able to watch what happens without other people knowing that you are there 做墙壁上的一只苍蝇，做不被察觉的观察者 I wish I’d been a fly on the wall during that conversation. 我真希望自己能神不知鬼不觉地偷听到那次谈话。
→ fly-on-the-wallbe a fly on the wall• I wished I could be a fly on the wall.• I wish I'd been a fly on the wall during that conversation.• You should be a fly on the wall and hear him sing your praises.• Oh, wouldn't I like to be a fly on the wall when you tell her the latest!
→ be a fly on the wall at fly2(4)