Let the Cat Out of Bag

The Definition

To "let the cat out of the bag" is to accidentally or carelessly reveal a secret. It marks the moment a piece of concealed information becomes public, often ruining a surprise or exposing a deception.

The Deep Dive

This idiom is widely believed to stem from a common type of livestock fraud practiced in 18th-century European marketplaces.

  • The Pig in a Poke: The phrase is closely tied to another idiom: "buying a pig in a poke" (a poke being an old word for a sack). In this scenario, a customer would purchase what they believed was a suckling pig. The merchant would bag the animal for easy transport, but unscrupulous sellers would sometimes swap the pig for a less valuable cat when the buyer wasn't looking.

  • The Revelation: The secret was only revealed when the buyer got home and opened the sack. Once the cat was out of the bag, the con was exposed, and the truth was impossible to hide or "put back" into the bag. While some historians find the logistics of this trick—such as the weight difference between a cat and a pig—suspect, the linguistic connection between "pigs in pokes" and "cats in bags" is well-documented in English, German, and Dutch.

  • Nautical Alternative: A secondary theory suggests the "cat" refers to the cat-o'-nine-tails, a whip used for punishment in the Royal Navy. The whip was kept in a red baize bag, and "letting the cat out of the bag" would imply that a sailor's transgression had been revealed, leading to the removal of the whip for punishment. However, most etymologists favor the marketplace origin as it aligns more closely with the theme of revealing a secret or a trick.

Fast Facts

  • First Printed Use: The first documented use of the phrase in its modern sense appeared in a 1760 book review in The London Magazine, where the reviewer complained that the author had "let the cat out of the bag" regarding the plot.

  • Global Versions: In Spanish, the equivalent phrase is dar gato por liebre ("to give a cat instead of a hare"), referring to a similar culinary fraud where cat meat was allegedly substituted for rabbit.

References

  • Ammer, C. (2013). The Dictionary of Clichés. Skyhorse Publishing.

  • Snopes. (2025). The Marketplace Fraud Theory of Letting the Cat Out.

  • Oxford English Dictionary. (2026). The Evolution of Livestock Metaphors.