隔墙有耳 Walls have ears
Explanation
比喻秘密的事情容易泄露，说话做事要小心谨慎。
A metaphor for how easily secrets can leak out; one should be careful and cautious about what one says and does.
Origin Story
从前，在一个古老的小镇上，住着一位名叫阿强的年轻木匠。阿强为人老实，手艺精湛，但他有个坏习惯：喜欢在工作间里自言自语，常常把自己的想法和计划都说了出来。有一天，他接了一单重要的活儿——为镇长打造一张精美的书桌。为了保密，他特意关紧了工作间的门窗。然而，不知为何，他设计的图纸和制作的计划，却总是被镇长提前知晓。阿强百思不得其解，直到有一天，他无意中发现，隔壁邻居老李的房间与自己的工作间只有一墙之隔，而且老李经常会凑在墙边偷听。原来，老李的听力非常好，即便隔着墙壁，也能清晰地听到阿强工作间里的动静。阿强这才恍然大悟，原来所谓的'隔墙有耳'是真的。从此以后，阿强在工作中更加谨慎小心，不再随意把自己的想法说出来，终于成功地完成了为镇长打造书桌的任务，再也没有发生过类似的事情。
Once upon a time, in an ancient town, there lived a young carpenter named Ah Qiang. Ah Qiang was honest and skillful, but he had a bad habit: he liked to talk to himself in his workshop, often revealing his thoughts and plans. One day, he took on an important job—to make a beautiful desk for the mayor. To keep it secret, he carefully closed the doors and windows of his workshop. However, for some reason, his designs and plans were always known to the mayor in advance. Ah Qiang was puzzled until one day he accidentally discovered that his neighbor Lao Li's room was separated from his workshop by only a wall, and Lao Li often listened at the wall. It turned out that Lao Li had excellent hearing, and even through the wall, he could clearly hear what was going on in Ah Qiang's workshop. Ah Qiang then suddenly realized that the saying 'walls have ears' was true. From that day on, Ah Qiang was more careful in his work, no longer casually revealing his thoughts, and finally successfully completed the task of making a desk for the mayor without any similar incidents.
Usage
用于提醒人们说话做事要谨慎小心，避免泄露秘密。
Used to remind people to be cautious in their words and actions to avoid revealing secrets.
Examples
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隔墙有耳，说话小心点！
gé qiáng yǒu ěr, shuō huà xiǎoxīn diǎn!
Walls have ears, be careful what you say!
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这可是隔墙有耳的地方，千万别说泄密了！
zhè kěshì gé qiáng yǒu ěr de dìfang, qiānwàn bié shuō xiè mì le!
This is a place where walls have ears, don't say anything secret!