A fiddler played at a trow wedding; he promised the trows a cow to take him home and they took the cow by magic.
Some trows [trolls, fairies] asked a fiddler to play at a wedding and took him away in a strange boat. As they rowed the trows said, "Trooly mooly o da warp." Each stroke of the oars took them three miles and in no time they were in Norway. It was a very pleasant company and the fiddler played all night then turned down the trows when they offered to take him home. When he was ready to go home, they said he would have to give them something for taking him, so he promised them a young cow.
They returned singing, "Trooly mooly o da warp," at every stroke. When he got home he discovered he'd been lost and given up for dead; it was three years since he had left. But he couldn't explain where he'd been. He was so annoyed he decided not to give the cow. But when he looked at the cows there was one sickly animal that neither ate or drank, and he realised that it was only the shape of the cow that was left: the trows had taken the real animal.