American Idiom - informal : Let the Cat Out of the Bag ~ revealing a secret by mistake or without intending to. br br Examplesbr br Max was supposed to be surprised about his upcoming birthday party, but his girlfriend let the cat out of the bag, and he now knows.br br The HR department was informed not to discuss about the layoff, but someone let the cat out of the bag.br br “How could you let the cat out of the bag?” his wife asked. “Now, I have to find her again so I can take her to the vet.”br Did you catch that? Trick phrase, the sentence is a practical situation.