Sometimes a market trader would put a cat in his bag and pretend it was a pig to fool the customer! So if someone lets the cat out of the bag, the secret would be open to us.

有时一个市场商人会把一只猫放在他的包里，假装它是一只猪来愚弄顾客！所以如果有人让猫从包里出来，秘密就会为我们所知。

youdao

Letting the cat out of the bag is supposed to stem from a trick played in old markets where buyers were duped when they thought they were buying a Suckling pig.

一般认为，“把猫从袋子里放出来”的说法源自古代集市上的一个把戏：有时，商贩会欺骗买家，在他们购买乳猪的袋子里装一只猫。

youdao

Your husband should have asked you first if it was okay to give your niece this information, but you can't put the cat back in the bag.

你的丈夫首先该询问你的意见，是否将此信息传达给你侄女是没问题的，但是你不能将猫房在袋子里。

youdao

"The only way to solve this is to put the cat back in the bag, " says Charles (Chip) Kahn, president of FAH.

FORBES: Bad Medicine

So after a lackluster year of falling profits and bad news, Nintendo seems to have pulled the cat out of the bag in time for Christmas.

FORBES: Skyward Sword is the Fastest Selling Zelda Game Ever

Although the identity of the winner is meant to be a closely guarded secret, the Cameroon striker let the cat out of the bag following their midweek friendly win over Senegal in France.

BBC: Caf award to go to Eto'o