In the Royal Navy the punishment prescribed for most serious crimes was flogging. This was administered by the Bosun’s Mate using a whip called a cat o’ nine tails. The “cat” was kept in a leather or baize bag. It was considered bad news indeed when the cat was let out of the bag.
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So how did that come to mean spilling the beans?
Maybe when you release the cat on a person they would spill the beans as a result?