As prison guards in one of Brazil's notoriously overcrowded and chaotic jails, the officers in Barra da Grota prison probably thought they had seen it all.
But last week they saw something that shocked even their hardened heads: a mouse, they noticed, was being used by inmates to courier drugs.
The animal was seen scurrying along the corridor with tiny bags of drugs tied to its tail, running between the cells.
Gean Carlos Gomes, director of the central Brazil prison, 1770km inland from Recife, said the mouse was being used as a "bridge" between cells.
"They attached a hook to the mouse's tail and then used it to carry the drugs and other goods from one cell to another," he said.
"When the animal arrived at its destination, the prisoner took the mouse and removed the hook from its tail."
Guards raided the cells and found 29 small packets of marijuana and 23 cocaine.
They are now scrolling through CCTV footage to try and discover which prisoner was the mouse's master.
The mouse was taken outside and released nearby.
It is not the first time that animals have been used to smuggle goods in and out of prisons - although cats, not mice, are generally the couriers of choice.
Brazilian prisoners in 2009 were caught using carrier pigeons to fly in contraband.
In January 2012, a cat was caught in Brazil while trying to slip through the prison gates with tools taped to its body, including a saw and drills.
In August 2012, police in Russia realised that a cat was being used to smuggle heroin into a prison. The cat was taken out of the prison by released inmates, who carried the animal in their bags and handed it over to drug dealers waiting outside the prison fence.
They stuffed the cat's collar with heroin and released the animal, which sneaked back into the prison.
Two years previously a cat attempting to enter a prison in the Russian republic of Tatarstan with heroin in its collar was killed by a prison dog.
A cat with mobile phones strapped to its body was seen entering a prison in Russia in June 2013.
And in October 2013 a cat was caught coming out of a prison in Moldova with heroin inside its collar.