Let the cat out of the bag

    泄露秘密

    A: I heard the surprise birthday party for Jim was a huge success.

    B: Yeah. Amazingly, not one of the people who knew about the surprise let the cat out of the bag.

    Note: This idiom means to "tell something that is a secret, often without intending to." One heard origin relates to the fraud of substituting a cat for a piglet at markets. If you let the cat out of the bag you disclose the trick. This form of trickery is long alluded to in the language and "pigs in a poke" are recorded as early as 1530. Versions of the phrase exist in both Dutch and in German, translating loosely as "to buy a cat in a bag," that is, to buy false goods.