"Cat is out of the bag"

hy2007

The truth has been exposed, there is no purpose to the deception
any more.

Usage Example
\"Well, the cat's out of the bag. I may as well tell you the whole story.\"

Origin
The origin of this is rather debatable. Supposedly, it was to describe
some unscrupulous butcher's deception. You order a piglet, and he gives
you this sack, which he said contains a piglet. You didn't think much of
it. You take it and walk home. On the way, the bag start to wiggle. You
open the bag to take a look, and a cat leaps out of the bag and disappears
before you blink. No piglet. Just a cat out of the bag.

On the other hand, how did the unscrupulous butcher got the cat into the
bag in the first place?

Chinese Equivalent
纸包不住火？