Circles on the field and other formations. China

A flock of sheep in China has been going around in circles for almost two weeks, and it seems that no one really knows why. The strange behavior was recorded by CCTV cameras at a sheep farm in northern China.

In a video released Wednesday by Chinese state-run news outlet People's Daily, dozens of sheep can be seen walking clockwise in a circle while other animals watch from outside the circle. Although it has been reported that the sheep look perfectly healthy, it is unclear whether the animals ever stop to eat and drink, and whether others take their place in the circle when this happens.

The owner of a sheep farm, who gave her name as Mrs. Miao, told reporters that the strange sight began on November 4 with a handful of sheep, but in the following days dozens of others joined them. Interestingly, although the farm consists of 34 sheep pens, only the sheep at number 13 behaved strangely.

A video of sheep walking in circles went viral in China shortly after being posted online by People's Daily, and several theories about the strange movement have since emerged. The most popular theory is that sheep are infected with a bacterium that causes a condition known as listeriosis, also called "circle disease".

According to the Merck Manual, "initially affected animals suffer from anorexia, depression and disorientation. They can huddle in corners, lean against stationary objects or circle towards the affected side."

However, the above theory has already been challenged, because sheep and goats suffering from listeriosis usually die within 14-48 hours after the first symptoms appear. The sheep in the viral video have been doing this for 12 days in a row, and they seem perfectly healthy.

Although this behavior is considered unusual, it is not unheard of. A similar situation occurred in 2108, when a hundred reindeer on the Kola Peninsula of Russia walked in a circle for no apparent reason.