Because they are chasing a giant ball of wool.
In a new video from the American Chemical Society, comedian and science communicator Derek Muller explains why sheep walk in circles. According to the comedian, sheep are not just spinning in circles because they’re bored or hungry. Instead, they’re chasing a giant ball of wool. The circle helps them keep their bearings as they move around.
Sheep have been known to form a circle and walk around it for many reasons. Some farmers believe that it’s an instinctual response to predators that might be lurking nearby. But as Muller explains in his video, sheep also walk in circles when they’re grazing on pasture that has been treated with an anti-fungal agent called amprolium.