Vikings hunting reindeer in Norway were once confounded by “reindeer cyclones”; a threatened herd would literally run circles around the fierce hunters, making it nearly impossible to target a single animal.

Faced with this spinning reindeer stampede, any predator — wolf, bear or human — would have a very tough time targeting and overpowering a single reindeer, making this a formidable defense strategy, according to a statement from PBS.

This behavior is also practiced by reindeer kept in corrals, occurring in groups of at least 20 to 25 animals, researchers wrote in a 2002 study published in the journal Rangifer. Penned reindeer formed “cyclones” and were observed to run “invariably” in a counterclockwise direction, the scientists reported.