Let the cat out of the bag
This expression dating from the 18th century means to disclose secret or confidential information, and is often attributed to the removal of the cat o’ nine tails from the canvas bag in which this infamous punishment instrument was kept. The trouble with the cat o’ nine tails theory is that it does not fit the context. 18th century naval floggings were very public events designed to deter others. There was nothing secretive about them. Therefore, it is improbable that removing the cat o’ nine tails from its bag should generate the meaning the expression has today. Another candidate theory is the fraudulent practice in English marketplaces of selling someone a cat or a pup in a bag instead of a piglet. This origin prompts suspicion. Anyone who has ever put a cat into a bag instead of a piglet would know that the difference is immediately perceivable. This theory does gain credibility, however, because of the French expression 'acheter un chat en poche', which means 'to buy a cat in a pouch', and the German 'die katze im sack kaufen', which means 'to buy a cat in a sack.' In both the French and the German versions, the emphasis is on the swindle itself, exhorting people not to buy a cat in a sack. Whereas in the English version, the emphasis is on exposing the swindle by letting the cat out of the bag. Generally, when one lets the cat out of the bag, it implies trouble, which is implicit in exposing a swindle. This explanation, therefore, has far more credibility than the cat o’ nine tails theory. Will Rogers, the American actor and comedian, once said, “Letting the cat out of the bag, is a whole lot easier than getting it back in.” He is absolutely right. See also Sold a pup and Pig in a poke.