That fantasy did not come from nowhere.
_ It was inspired by a real story in the autobiography of Nikita Khrushchev’s official translator.
_ At those summit meetings each leader brought their own translator.
_ The Western leader (I cannot remember who) was uneasy with a proposal that Khrushchev made, so the Western leader said
we would not like to buy a pig in a poke
to which the answer came back via the other translator
the cat that drinks your milk will also catch your mice
There was immediate panic between the two translators who then had to explain to all and sundry that there was this Medieval European story of a farmer who went to market and swapped eggs for a suckling pig.
_ The farmer did not know that the trader was a fraudulent person.
_ The trader went to a lot of trouble to put the little pig into a bag (an old word for bag is a poke) and urged the farmer not to open the bag until he was safely home.
_ When the farmer did open the bag to show his wife - out jumped a cat.
_ There are two relics of this story in the English language which are the following rather vague words (pretending to be gems of wisdom) that are occasionally used by one’s elders and betters
don’t let the cat out of the bag
and
don’t buy a pig in poke