The title is a very common expression used by many people and Chat Noir and Ladybug. It usually implies that a secret is out or known by a few more people. Thus, the 'out of the bag' part. But here's my question:
How do you even get the cat IN the bag?? How do you even FIND a cat to put it? And why do you put a CAT in a BAG? Won't the cat just make a mess of the bag's insides?