Spies in the Stalin regime 'inspected the excrement of foreign leaders' in a bid to extract information.
It was a top secret Soviet experiment that was definitely not to be sniffed at.
According to a report in a Russian newspaper, special lavatories were installed for Mao's 10-day visit in order for the Chinese leader's stool to be collected in secret boxes instead of the sewers.
His excrement was then whisked off for analysis, former Soviet agent Igor Atamanenko claims.
"In those days the Soviets didn't have the kind of listening devices which secret services do today," he told the newspaper. "That's why our specialists came up with the most extravagant ways of extracting information about a person."
Which begs the question: what exactly were the Soviet scientists hoping to glean from Mao and other foreign leaders' poo?
"For example, if they detected high levels of amino acid Tryptophan, they concluded that person was calm and approachable," Mr Atamanenko told the BBC.
"But a lack of potassium in poo was seen as a sign of a nervous disposition and someone with insomnia."
"A lack of potassium in poo was seen as a sign of a nervous disposition and someone with insomnia" Former Soviet agent Igor Atamanenko
Historian David Halberstam wrote about the December visit in The Coldest Winter, claiming Mao was housed in the old Metropole Hotel that was usually used for minor dignitaries.
It seems Stalin's successor, Nikita Khrushchev, didn't share his enthusiasm for excrement espionage. According to Komsomolskaya Pravda, one of Russia's most popular dailies, the project soon went down the pan.