“Buy a pig in a poke”in other languages

Same idea, different pictures

All five warn against the same market trick, as the story goes: a seller offered a piglet in a sack (a “poke”), and a buyer who didn't look got home with a cat. Swedish and English keep the pig, köpa grisen i säcken. French, German and Polish name what was really inside: acheter chat en poche, die Katze im Sack kaufen, kupować kota w worku.

The same trick explains the English let the cat out of the bag: open it, and the secret is out.