Drugs, tobacco and mobile phones were smuggled into a prison stuffed inside dead rats.
The items were sewn inside the bodies of three rats found by officers in early March in the grounds of HMP Guys Marsh near Shaftesbury, Dorset.
It was the first recorded instance of rats being used in that way, the Prison Service said.
It said it was investigating with Dorset Police but was unable to say whether anyone had been arrested.
Warning: Graphic image below
Prison officers cut open the rodents, which had apparently been thrown over the fence, and found a large amount of drugs, including spice and cannabis.
They also discovered five mobile phones and chargers, together with three Sim cards.
The items were intended to be collected from the grounds and sold to inmates, the Prison Service said.
Prisons Minister Rory Stewart said: "This find shows the extraordinary lengths to which criminals will go to smuggle drugs into prison."
Previously drones, tennis balls and pigeons have been used by prison smugglers.
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In June 2018, Dorset's senior coroner said the use of drugs at HMP Guys Marsh was "rife", leading to a number of recent deaths.
The Prison Service said it was planning to replace windows at the jail to stop drugs being moved between cells.
It also said an extra 12 prison officers were supporting inmates with substance misuse problems.