【成语来源】 

walls have ears
隔墙有耳

Once upon a time, there was a curious man.
从前,有一个好奇心很重的人。

He liked to gossip about other peoples' privacy.
他总是喜欢四处打听别人的秘密。

He knew too many secrets and found it hard to keep them all.
他知道的秘密太多了,憋在心里很难受。

One day he drank several cups of wine, and while drunk spilled all the secrets.
一天,他喝了几杯酒,结果把自己打听到的事情全部说了出来。

To his surprise, the man next door heard all he said.
他没想到,隔壁房间里的人听见了他说的话。

Very soon, everyone knew of his bad habit of gossiping.
没过多久,所有人都知道了他多嘴的坏毛病。

The walls may not have ears, but the person next door does. "This idiom is often used to alert people to be careful about their words.
墙壁虽然没有耳朵,但是隔在墙另一头的人有,这个成语现在常常用来告诫人们要谨言慎行,不要说三道四。

【文化链接】

“隔墙有耳”形容了“墙上长了耳朵”的样子,巧的是,英语中还真的有“walls have ears”(墙壁长耳)。
据载,“walls have ears”首见于希腊。传说古希腊国王Dionysius(狄奥尼西奥斯,统治着西西里最富庶的城市Syracuse)实施独裁,其手中至宝 ——耳状岩洞,可以连通整个皇宫。凭借“耳朵”岩洞,皇宫里便没有秘密,所有言语全在狄奥尼西奥斯的监听范围之内。
也有说法认为,“walls have ears”始于巴黎卢浮宫。卢浮宫原为法国王宫,据说其墙壁中安装有神秘的传声管道,可供偷听使用。王后凯瑟琳摄政时期,就是靠这种“有耳”的墙壁来偷听可疑大臣的言谈的。
大约在17世纪20年代,“walls have ears”正式进入英语词汇,用以比喻秘密也会泄露,或是告诫人们说话留心,免得被偷听。

我们一起来看两个例句:

Be careful what you say; the walls have ears!
说话要小心,隔墙有耳啊!

Hedges have eyes and walls have ears.
篱笆有眼,隔墙有耳。