Where Does the Phrase “Let the Cat Out of the Bag” Come From?

Why was the cat in a bag in the first place?

One of the most curious and funny aspects of language is the use of idioms. These expressions use words in a non-literal way to mean something other than the actual meaning of the individual words—and they’re often quirky and funny. (And that’s not unique to English—check out these international idioms that sound hilarious in English.)

And, notably, a lot of them involve animals, from “straight from the horse’s mouth” to “let the cat out of the bag.” When we say “let the cat out of the bag,” we’re not actually talking about a feline that was in a bag (hopefully!) but about a secret or surprise that was revealed. What’s the origin of that idiom?

Where did this phrase come from?

Well, first, let’s consider the first recorded use of the phrase. In a 1760 book review in the London Magazine, the reviewer complained that he “wished that the author had not let the cat out of the bag,” presumably referring to some kind of plot point.

But while the first recorded use of the phrase is pretty straightforward, its origin is not. Unfortunately, it’s hard to pin down a precise origin for many idioms like these, simply because of the way language evolves. People start using phrases gradually, over time, and there’s no concrete historical record of how they came up with that phrase. This is especially the case with figurative expressions, which, by definition, don’t literally mean what they say.

So there’s no definitive consensus as to where it comes from, but there is an explanation that most linguists consider at least somewhat likely. And it actually, literally, involves cats in bags!

The medieval scam explanation

The most popular explanation for why we say “let the cat out of the bag” dates back to the Middle Ages. As the story goes, shady livestock vendors in medieval marketplaces sought to swindle their buyers. When someone would purchase a pig, the vendor would sneak a cat into the bag instead, cheating the buyer out of the higher price for a pig. It wasn’t until the buyer arrived home and, literally, let the cat out of the bag that they’d realize they’d been scammed, hence the phrase’s association with revealing a secret. English has no shortage of idioms for telling a secret—here’s why we also call it “spilling the beans.”

This explanation is not outright proven—and neither, in fact, is the tale that medieval vendors even regularly did such a switcheroo. (Would the weight difference between a pig and a cat not clue buyers in, Mental Floss even wonders?)

But this explanation does have some things going for it. For one thing, per Phrases.org, both the Dutch and German versions of this phrase translate to “to buy a cat in a bag,” which alludes a little more directly to a deceitful purchase. And the Spanish translation means “to give a cat for a hare,” suggesting (somewhat more plausibly) that it would be rabbits, not pigs, that vendors would switch with the cats.

But, then again, the expression “pig in a poke,” which dates back to the 16th century, also refers to making a deal or purchasing something without fully validating it. (And a “poke” is an old-timey word for a bag.)

The nautical punishment explanation

There’s another theory about the origins of this expression, and it’s a good deal darker. This explanation claims that the “cat” the expression refers to is not a feline but the “cat o’ nine tails,” a whip made from nine intertwined cords that was used as a form of punishment in the British Royal Navy and in prisons until as late as the 1840s. It was called a “cat” because the marks it left on its victims resembled scratches. (In fact, it’s also a likely candidate for the origin of “cat got your tongue.”) If you dare, learn about more English idioms like this with surprisingly dark origins.

But there are a few details that diminish this explanation’s likelihood. For one thing, there are no records of the actual phrase, “let the cat out of the bag,” being used in reference to nautical exploits. Not to mention that the cat o’ nine tails punishment, while certainly notorious and unpleasant, wasn’t really a secret, per se. Next, find out the stories behind 14 more common expressions we use all the time.

Meghan Jones
Meghan Jones is a Staff Writer for RD.com who has been writing since before she could write. She graduated from Marist College with a Bachelor of Arts in English and has been writing for Reader's Digest since 2017. In spring 2017, her creative nonfiction piece "Anticipation" was published in Angles literary magazine.