To let the cat out of the bag means to reveal a secret, often by accident.
One possible origin comes from old market scams in which a seller might secretly replace a valuable piglet in a bag with a worthless cat. If the bag was opened and the cat escaped, the trick was exposed.
One possible origin comes from old market scams in which a seller might secretly replace a valuable piglet in a bag with a worthless cat. If the bag was opened and the cat escaped, the trick was exposed.
She let the cat out of the bag about the surprise party before we could stop her.