MUNDANE MYSTERIES: Why Do We “Let The Cat Out Of The Bag”?

We’ve all heard the phrase, “Whoops, I let the cat out of the bag” when someone accidentally reveals a secret. But where did that phrase come from? And who put that cat in a bag to begin with?

The phrase’s first documented usage was in a book review in The London Magazine back in 1760: “We could have wished that the author had not let the cat out of the bag.” That, unfortunately, is about all we know for sure. There are 2 popular origin stories for the phrase, but both seem pretty implausible.

The first claims the phrase refers to the cat o’ nine tails, a whipping implement infamously used by the Royal Navy as an instrument of punishment aboard its ships. The whip’s nine knotted cords could scratch an undisciplined sailor’s back badly, hence its feline nickname. The bag comes into play because the cat, being made of leather, had to be kept in a sack to protect it from drying out in the salty sea air & keep it flexible.

The other explanation is that it was born from a ridiculous bit of livestock fraud. Supposedly, merchants would sell customers live piglets, and, after putting a pig in a sack for easier transport, would sometimes swap the pig for a cat when the customer wasn’t looking. The buyer wouldn’t discover they’d been cheated until they got home & literally let the cat out of the bag. Yet, while pigs were bagged for sale, there doesn’t seem to be any recorded evidence that that kind of con-game was commomplace.

There’s a certain implausibility to that trick, though, as piglets big enough for market have different sizes & builds than cats. Also, cats meow, they don’t oink. It’s hard to imagine enough people picking up their purchase and thinking, “this sack seems a bit light, and isn’t making the right noise, but I guess everything is normal,” to create an idiom out of it.

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