Sam O’Brien at Atlas Obscura:
In the winter of 1984, Timothy Tangherlini worked on a dairy farm on the Danish island of Funen. One day, while brushing cattle in the barn, he spotted a tiny man in a hat sitting on the back of one of the cows. When Tangherlini tried to speak to the stranger, the little man jumped out the barn window. Assuming it was a trick, he told the couple that owned the farm about the encounter. They both shrugged. “That was the nisse,” they explained.
Tangherlini is now a professor of Scandinavian folklore at UC Berkeley. Whether or not one truly believes the tales, the barn-dwelling “house elves” often known as nisse have been figures in folklore across the Nordic region since at least the late Middle Ages. Farmers believed that surviving a hard winter depended on the nisse’s whims, which were mercurial. Keep your farm’s nisse happy, and he’d make sure your milk stayed fresh and your livestock remained healthy. Disrespect him, and you might find your cow dead in the morning.