Where does the expression “let the cat out of the bag” come from? 

Idioms, phrases and expressions inject daily conversations with colour and life. This is because almost all of them carry a fascinating backstory about how their meaning evolved over time and became a part of modern speech. One such expression that is used commonly is “let the cat out of the bag.” Surely, while speaking, the speaker does not have a bag on his shoulders with a cat hidden it. Then why do we use it? Read on to learn more about the origin behind it. 

What does “let the cat out of the bag” mean? 
Of course, there is no feline friend here who jumps out of a bag. “Let the cat out of the bag” means revealing a secret or surprise, either by an accidental slip of tongue or on purpose. Most often, however, it occurs without the intention of disclosing hidden information. Depending upon the situation, this could refer to the revelation of a conspiracy, spilling a secret, spoiling the plot of a movie or book, etc. Example: Alex let the cat out of the bag about his brother’s graduation party.” 

Where does this expression originate from? 
It is believed that during the Middle Ages, vendors, especially those who sold livestock in marketplaces, were not considered to be the most honest people in town. They were known to swindle and deceive their customers quite regularly. When a customer purchased a pig from them, they would discreetly replace it with a cat. This way, the customer would believe to have bought a pig, which was higher in cost, but would actually go home to discover that they had been scammed. Quite literally in this scenario, they would open their bag to find a cat. Although popular, the authenticity of this theory remains uncertain as there is no clear evidence to support it. 

An alternative theory about the origin of this phrase is the nautical one. England’s Royal Navy used cat o’ nine tails as a torture and punishment instrument while out at sea. A cat o’ nine was a whip which had nine knotted cords, whose lashes were tipped with metal or barbs- leading to agonising pain. The cruel contraption was used to discipline sailors who were not doing their job adequately. The salty sea breeze often caused the device to dry out. In order to prevent this, it was kept in a bag/ sack. Thus, one can draw the connection between a “cat” o’ nine and they bag it was kept in. However, the problem with this theory is that it does not seem to address the fact that there is a secret that is being revealed. It nods towards an incoming punishment instead.