let the cat out of the bag
（无意中）泄露秘密
to tell a secret carelessly or by mistake
俚语来源
古代集市不诚信的卖猪人常常把猫装在口袋里冒充小猪卖给别人，粗心的买主如果不打开口袋便不会发现，但是如果猫从口袋里钻了出来，这个骗局就暴露了。
例如：
Be careful not to let the cat out of the bag. It's supposed to be a surprise party.
小心别说漏了嘴，这是个惊喜派对。
I wanted it to be a surprise, but my sister let the cat out of the bag.
我想给大家来个惊奇，可我妹妹却先说漏了嘴。
I wanted mother's present to be a secret, but my sister let the cat out of the bag.
给母亲的礼物我原想保密，可是妹妹却露了马脚。
It's a secret so please don't let the cat out of the bag.
这是一个秘密，因此请不要泄露秘密。
How did Mom find out we were planning a surprise party for her? Who let the cat out of the bag?
妈妈是怎么知道我们要为她准备一个惊喜派对的?谁泄露了秘密?
They let the cat out of the bag by revealing their upcoming product. 他们不小心透露了他们即将推出的产品。
Oh no, you let the cat out of the bag! Now the surprise is ruined.糟糕，你泄露了秘密！现在惊喜已荡然无存。
I've let the cat out of the bag already, Mr. Li, and I might as well tell the whole thing now.
李先生，我已经无意中泄露了秘密，干脆现在就把全部情况都告诉你。
