“Mind you,” she said through her tears, “that man who came to us one time, when we dwelt at Skog? He that knew all the ancient lays? Mind you the lay of a dead man that was come back from the world of torment, and told his son the story of all that he had seen? There was heard a groaning from Hell’s deepest ground, the querns of untrue women grinding mould for their husbands’ meat. Bloody were the stones they dragged at — bloody hung the hearts from out their breasts ”
The above paragraph is a part of 'Kristin Lavransdatter' by Sigrid Undset. It's a conversation between husband and wife. The wife is saying about a saga or similar thing, repenting her past. The novel was written 1929, depicting 14 century Norway, which was translated from Norwegian to English in 1929 by Charles Archer in a rather old fashioned way.
My general understanding for the above is 'unfaithful wives will be punished in Hell', but I can't figure out in what manner they are punished. (In fact, I don't understand the exact meaning of those bold part of sentence I marked.)
Hoping somebody could help me.