I'm not exactly sure what the phrase, "The cat's out of the bag" is supposed to mean.
I mean, who puts a cat in a bag in the first place? I think a bag would be the last place I'd put a cat. It's not like any cat is going to go into a bag peacefully.
And imagine what it'd be like to let the cat out of the bag! I'm sure it'd come flying out of that bag like a bat out of hell, claws a blazin'.
In all reality, I do know what the phrase means. But who coined it? Who thought, "Well, I've had this secret, and I finally told people. How could I say that? Hmmm...Got it! 'The cat's out of the bag!' Definitely the best way to put it."
My opinion? Not really.