A Tilberi ("carrier"), or Snakkur ("spindle"), is a familiar creature from Mythic Iceland. AKA "Dust Bunny", "Poppet".
Tilberi are created by a häxan (witch-woman) from a large straight bone from a freshly-dead human corpse wrapped in wool by the light of a full moon. For three weeks, the witch will warm it between her breasts and feed it mead or wine that has been blessed by a Pagan or Christian priest by spitting the alcohol on the Tilberi. By the second week, the Tilberi begins to move (which can attract attention if the witch is not careful), and by the third week, it comes to life, after which it must be suckled on blood from its creator's teat (a mole or cut, usually on the witch's thigh).
The Tilberi resembles a woolly creature with two heads, one at each end of the bundle, and sharp teeth in tiny and monstrous faces resembling that of the corpse. When at home, the Tilberi clings to the witch's teat and drinks the witch's blood. The Tilberi can speak in languages known to the corpse and/or witch in a thin, childish voice. It can be instructed to go forth into the night to run simple errands for the witch, usually involving acts of petty theft (milk, wool, small objects such as coins or jewelry), delivering messages, spying on others, or committing other minor acts of mischief and mayhem. The Tilberi, in drinking her blood, drains the witch a little more every day until she eventually dies, unless the Tilberi is killed. The only ways to kill a Tilberi are to order it to undertake a very difficult task that it will work itself to death to complete (such as eating all the droppings in a large sheep pasture) or to burn the witch and Tilberi together at the stake.
If its mistress dies before it returns from its mission, the entity might go insane, feeding on the blood, hair, and wool of any farm animals or people it encounters, then rolling in sheared or ripped-out hair and wool to form a ball and growing to prodigious size, until it is big enough to begin consuming corpses and killing victims for food.
A similar creature is the Trollnøste ("troll cat") or Mjölkhare ("milk rabbit"), a familiar which usually appears in the form of a large ball of wool, hair, wood shavings, and/or finger/toe-nail parings, or sometimes in the form of a woollen cat or rabbit, shaped by the witch and animated with witch's blood.