Task: Text Categorization
Input (English): In one story, a barbarian king seeks this item out by cutting out the heart of a man who is so brave that his heart doesn't quaver with fear. This item is sought by King Atli from Hogni, though it originally belonged to a creature that died after a man dug a pit and hid in the hole so that he could avoid its blood. A body that is stuffed with this material is given to (*) Hreidmar after Loki mistook Otr for an otter. A story involving the god Ran lead the phrase "brightness of the sea" to be a kenning for this substance. Draupnir is an item that is made of it, as is the bristles of the boar Gullinbursti. For 10 points, name this treasure that comprises Sif's hair, hordes of which are guarded by the dragon Fafnir.
Output (English): Social Science