The bisterk thing is a demon from the Heligoland tradition. If someone has an accident at sea, this demon should rise from the water and lie down on stairs or crawl in the corners of a barn. He is mostly described as a black monster with plate-sized eyes and the fur of a sheep . He should move on rolling.
A Heligoland saying goes: "Det bisterk thing was on the way" and is used when you are hit by misfortune.
- Leander Petzoldt: Small lexicon of demons and elemental spirits , 3rd edition Munich 2003, page 43 ISBN 3-406-49451-X
- Benno Eide Siebs and Erich Wohlenberg: Helgoland and the Helgoländer , Kiel 1953