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。

《牛津词典》

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。

youdao

We planned to give her a surpriseparty, but he let the cat out of the bag.

我们计划给她一个令人惊讶的派对，但是他把事情泄露了。

youdao

Just be careful not to let the cat out of the bag, or someone may leave you holding the bag.

VOA: special.2009.01.25

If you tell about something that was supposed to be a secret, we say you let the cat out of the bag.

VOA: special.2009.09.27

The phrase to be left holding the bag is as widely used as the expression to let the cat out of the bag.

VOA: special.2009.01.25

Construction and Housing Minister Ariel Attias let the cat out of the bag.

CENTERFORSECURITYPOLICY: Netanyahu's perilous statecraft

They let the cat out of the bag only because there were all these rumors about JFK and other extracurricular activities.

NPR: 'First Off the Tee': White House Golf Tales

But at that point he let the cat out of the bag, or should I say pulled the rabbit out of his hat.

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