Don't let the cat out of the bag

This phrase generally means ‘to disclose a secret.’ You may hear this phrase used when you are about to reveal something and someone will tell you don’t let the cat out of the bag. The origin of this phrase appears to have two different sources.

The first source comes from around the 16th century when people bought pigs at the market. These pigs came in a bag and this lead to the expression pig in a poke (bag). Some unsavoury merchants would sometimes put a cat inside the bag instead of the whole pig, in order to trick unsuspecting buyers. This allowed the merchants to cut down on their costs.

The cat o' nine tails

The second source of this phrase comes from the cat o’ nine tails. This device, often known as the cat, was a common means of punishment in various militaries starting around the 17th century. When men broke the rules they would receive numerous lashes across the bare back. The cat was kept in a bag and would only be removed when someone was about to be punished. Applying the phrase don’t let the cat out of the bag is a little tricky because the meaning ‘to disclose a secret’ does not directly apply. However, in one regard this phrase does apply to the meaning because for new recruits the first time the cat was revealed to them it meant that the secret of the cat was now disclosed.

If someone is about to reveal a secret and you use this phrase don’t forget about the dead cat in the bag or the crack of the whip.