The idiom "哪壶不开提哪壶 (nǎ hú bù kāi tí nǎ hú)" literally means "to pick the kettle that is not boiling." It's used to indicate that someone is saying or doing something that shouldn't be mentioned in front of others, or that someone is bringing up a sensitive subject.
Idiom Story:
Hěn jiǔ yǐqián, yǒu fùzǐ liǎ kāi le jiān xiǎo cháguǎn. 很 久 以前,有 父子俩 开了 间 小 茶馆。 A long time ago there was a father and son who owned a tea-house.
Dāngshí de zhīxiàn Bái lǎoye tāncái hàolì, jīngcháng lái bái hē chá. 当时 的 知县 白 老爷 贪财 好利,经常 来 白 喝 茶。 The local official, Mr