Let the Cat Out of the Bag By EvilAugust 13, 2014February 25, 2020Popular Expression Let the Cat Out of the Bag = reveal a secret carelessly or by mistake Ex: Sarah didn’t know about her surprise party until someone was talking to her and accidentally “let the cat out of the bag.” Ex: We were going to keep our plans to get married a family secret, but my mother “let the cat out of the bag.” BACK to Popular Expressions