Tanngrisnir and Tanngnjostr are in Norse mythology goats who pull the chariot of Thor, the god of thunder. They are mentioned in the Elder Edda, compiled in the 13th century on the basis of earlier sources, and in the Younger Edda, written in the 13th century by Snorri Sturluson.
The Younger Edda tells us that Thor kills his goats every night, boils their meat and eats them, leaving their bones intact, but then uses his hammer to bring them back to life the next day, so that the goats are an inexhaustible source of food for him.
The same source tells us that Thor once spent the night with the peasants and shared the meat of his goats with them, but forbade them to touch the bones. But Tjalfi, the host's son, disobeyed and broke one of the bones to suck the marrow out of it. In the morning Thor revived the goats and, finding that one of them was limping, he forced Tjalfi and his sister Röskva to serve him for life as punishment.
Some scholars trace the image of the goats to the mythological boar Sehrimnir, who is slain and eaten every night in Asgard by the Aesir, but who then comes back to life.