Mystery Manor Adventure Forum

The phrase "A pig in a poke", which has been commonly used to describe a situation of helplessness and/or impending doom is derived from medieval times when the markets would sell pigs tied up in bags. The bags were often called "pokes".

Often times scammers would put cats instead of pigs in the bags and to avoid being scammed some buyers would open the bag to check, hence they "Let the cat out of the bag" a term now used to describe revealing or exposing a secret or ruse.

I've always understood 'the cat's out of the bag' -
refers to the British Navy in the early days - when sailors were often flogged for misdemeanours with a cat-o'nine-tials.
This being a sort of whip - with nine knotted ropes coming from the end.

If a punishable misdemeanour was discovered - the 'cat' was removed from the bag (this bag was tied to the main mast) -
and the expression - 'the cat's out of the bag' meant you'd been found out and trouble would follow.

Lots of English expressions are derived from the nautical history -
'sailing close to the wind'. a 'round robin', there are whole books devoted to these expressions - they are fascinating.