Today’s blog is inspired by my cat. She likes to explore all the opportunities available to her in a modest apartment. She loves boxes, wardrobe shelves and sleeping under the bed when the sky thunders. Yesterday I found her in my travel bag that I’ve been using for gym. As it was lying outside of the cupboard, she placed herself inside it, taking ownership as only cats can. This immediately made me think of the idiom, letting the cat out of the bag.
Not everyone can keep a secret, hard as they might try. And suddenly it just slips out. A half-sentence here, a careless comment there, and despite best intentions, what was meant to be closely held is out in the open. That moment has a name: “letting the cat out of the bag.”
Fraud
The origin story is less playful. One widely accepted theory traces the idiom back to medieval markets, where unscrupulous traders would swap a valuable piglet for a far less desirable cat, sealing the animal in a bag before sale. The deception only came to light when the buyer opened the sack – and out leapt the wrong creature. Fraud exposed, quite literally. In this reading, “letting the cat out of the bag” isn’t about gossip so much as it is about revealing a trick, a con, a truth someone hoped would stay tucked away (Phrase Finder; Brewer’s Dictionary of Phrase and Fable).
Linguists cautious
Another, slightly more nautical theory links the phrase to the cat-o’-nine-tails – a whip used for punishment aboard ships. The “cat” was kept in a bag, and taking it out meant discipline (and pain) was about to be administered. While vivid, linguists tend to treat this explanation with caution; it doesn’t align as closely with the idea of accidental disclosure (Oxford English Dictionary notes on idiom usage; Phrase Finder).
Out is out
Today, the phrase has softened. It’s alive in everyday conversation, far removed from livestock scams and shipboard justice. We use it when someone spills a secret (“I think Jess let the cat out of the bag about the party”) or when a carefully planned reveal is undone. There’s no malice required – just a moment of loose lips and a story that can’t be stuffed back in.
No alternative
What keeps the idiom current is its imagery. Unlike more clinical alternatives – “disclose,” “reveal,” “divulge” – this one has texture. It moves. It scratches. It refuses containment. And perhaps that’s why it endures: because secrets, like cats, are never entirely obedient.
Research assisted by AI
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