'Let the Cat Out the Bag'

The phrase oft used when someone lets a secret slip out- means that the suggested origin of magicians, at a fare or show, swapping a 'pig in a poke' for a cat as part of their magic act is more plausible than the nautical explanation of the 'cat o nine tails' being kept in a bag and brought out to administer punishment on board ship - tomorrow 'pig in a poke' and 'cat o nine tails' - only kidding !