Scientists have finally solved a mystery that has baffled them for a century - why does Swiss cheese have holes?
The old wives' tale claimed mice were responsible - but it turns out the culprit is hay.
These "microscopically small hay particles" get into the milk and create holes as the liquid matures into cheese.
The discovery also solves another riddle - why the famous holes in cheeses like Emmentaler or Appenzeller have been getting smaller or disappearing completely over the last 15 years.
It is because the milk has been getting cleaner.
The Agroscope institute claims the transition to fully-automated, industrial milking systems had caused holes to decline.
"It's the disappearance of the traditional bucket," said spokesman Regis Nyffeler.
Researchers at the government-funded body carried out tests in which they added different amounts of hay dust to milk.
Agroscope said the subject had been under study since at least 1917.