The seemingly strange phenomenon of a flock of sheep walking in a circle for what has been reported to be 12 days in Inner Mongolia may have a very simple explanation.
A video posted to the Twitter account of the Chinese state-affiliated People's Daily last week said that the flock of sheep had been walking in an almost concentric circle for more than 10 days on a farm in the China-controlled territory.
At the time, the media outlet said the cause of the behaviour was a mystery.
The internet rushed to fill the void, with some suggesting there was an X-Files episode in the making, or that the sheep had entered a "death spiral" (that's not a thing), while others suggested it was merely sheep doing what sheep do and following the leader.
A more plausible explanation was the sheep were suffering from listeriosis — a neurological infection caused by a bacteria commonly found in cattle feed and soil, and more often in rotting vegetable matter and mud.
The Listeria monocytogenes bacteria causes an asymmetrical infection in the brain stem, which can result in one side of the animal's face becoming paralysed and incessant circling, earning it the nickname "circling disease".
However, there are a number of giveaways that circling disease is not behind the behaviour seen in the video, according to Andrew Fisher, a professor of cattle and sheep production medicine at the University of Melbourne.
"They'd show a variety of circling and other neurological conditions and they'd get quite sick — some would die," Professor Fisher said.
"The way it usually manifests is not in half the flock — it's sort of between 1 and 10 per cent might be affected."
Animals suffering from listeriosis also don't move in concentric circles, but loll in their own pattern.
If it quacks like a sheep
Professor Fisher said there was an outside chance that the animals had developed a behavioural response to being kept in a small confined area.
He said that in the past when zoo animals were kept in small enclosures with little stimulus, they could exhibit "stereotypical pacing".
"In that scenario, they have a very defined or consistent, unvarying pathway."
However, he said while we can't say for certain, there's a more likely explanation.
"One suspects there's more going on behind the video that we don't see," he said.
Emma Doyle, a livestock expert and lecturer at the University of New England's School of Environmental and Rural Science, put it more bluntly.
"As soon as I looked at it, I thought, 'I've never seen sheep act like that,'" Dr Doyle said.
"It seems a bit dodgy. It looks sort of set up where they've put something in the middle to stop them going in."
Dr Doyle said it would be highly unlikely for sheep to form such a perfect, concentric shape, without some sort of interference.
The other, bigger problem though is that several media sources reported the animals were doing circles "non-stop" for 12 days.
"They're not going to go 12 days without water and food," Dr Doyle said.
The implication then is that the animals are leaving the circle for food and water before rejoining.
"It's very mysterious and at first look, a little hoax-y to me," Dr Doyle said.
"If it's real then I stand to be corrected."
