"Let the Cat Out of the Bag" — a Market Scam?
Picture a medieval market. You've haggled for a piglet, the seller hands you a wriggling sack, and you walk home pleased with yourself. You open the sack. A furious cat exits. Somewhere behind you, a con artist is already three villages away. Great story — but did it actually give us the phrase?
"Let the cat out of the bag" means to reveal a secret, usually by accident. The best-supported theory links it to the pig-in-a-poke scam — a worthless cat swapped for a piglet in a sack, exposed the moment the bag opened. First found in print in 1760. The rival naval theory doesn't survive contact with the meaning.
First, the pig in a poke
The scam itself is documented centuries before the cat idiom. English proverb collections from the 1500s already warn buyers not to purchase "a pig in a poke" — a poke being a sack — because what's inside might not be what was promised. The advice is simple: open the bag before you pay. Versions of the same warning exist across Europe, and several languages spell out the punchline: in German, buying blind is buying "die Katze im Sack" — the cat in the sack.
That continental echo matters. German and Dutch both let the cat out of the sack to mean revealing a secret, exactly like English. When three languages share one oddly specific image, the odds improve that the image comes from a shared, real practice — dodgy livestock markets were nothing if not international.
1760: the cat goes public
The English idiom's first known appearance is a book review in The London Magazine, 1760:
"We could have wished that the author… had not let the cat out of the bag." — The London Magazine, 1760
Note the casual use — no explanation offered, which means readers in 1760 already knew the expression. As always, the phrase is older than its paperwork. What we can't do is draw a documented line from the 1500s scam warnings to the 1760 idiom; the connection is plausible, cross-linguistic, and unproven. Honest grade: probable, not certain.
The rival story says the "cat" is the cat o' nine tails, the naval whip kept in a cloth bag — taking it out meant a flogging was coming. It's a real object with a real bag, but the meaning collapses: removing the whip revealed no secret, it announced a punishment everyone could already see coming. When an origin story matches the words but not the meaning, it's decoration, not etymology. (Compare the flogging story that actually does fit, over at bite the bullet.)
Why this cat stayed out
Like every idiom that survives, this one names a permanent feeling with a perfect picture: a secret, once released, cannot be re-bagged. Anyone who has ever blurted out a surprise party knows the physics — the cat does not go back in. Its cousin "spill the beans" covers the same territory with a messier picture, and if you're wondering why the cat keeps showing up in English idioms generally, we count the whole clowder in why are so many idioms about cats?
Citations and the full debate live at the Phrase Finder, with modern definitions at Merriam-Webster.
Quick FAQ
What does the phrase mean?
To reveal a secret — usually carelessly, spoiling a surprise or exposing a scheme.
Is the market-scam origin true?
It's the best-supported theory — backed by the documented pig-in-a-poke scam and identical idioms in German and Dutch — but the direct link is unproven. We grade it probable.
What about the cat o' nine tails?
Rejected by most references: taking out the whip announced punishment, it didn't reveal a secret. The meanings don't line up.
When was it first written down?
1760, in The London Magazine — used casually, so the spoken phrase is older.
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The IdiomJar team researches phrase origins from dictionaries, digitized newspaper archives, and the work of etymologists — and clearly labels anything that's folklore rather than fact. Read more about how we work.