Where did the expression "let the cat out of the bag" come from?

It's one of the phrases listed on this site. Unfortunately you'll have to select it from the list. I can't make it go straight to "your" answer.

Why not, Ewood? I can

Touché. I didn't spot the last part of the URL with the code for the specific point.

Ewood, just right click any hyperlink and choose 'properties'. There you will find the actual path.

or easier yet, chose 'copy shortcut'

Smartypants.

The explanation usually given for this expression seems bizarre, doesn't it ? The same goes for 'buying a pig in a poke'.Somehow it does not seem likely; perhaps our ancestors were very trusting or careless.If so, then the ancient French were the same.The expression 'acheter chat en poche' means exactly the same as our 'pig' one, 'to buy blind'. It translates as 'to buy cat in sack' and it too is still current and puzzling students of the language

I believe the two sayings are directly related.
'Buying a pig in a poke' implies deception, in that there is no pig in the poke (sack). One could not pull this one off with a completely empty poke, so a cat might be substituted.

'Letting the cat out of the bag' is when the whole thing breaks down and the truth becomes known and the cheater gets hit in the mouth.