So she had given out whoever could ride that flame should have her to wife. So when Gunnar and Hogni reached it, Gunnar rode at it, but his horse, good though it was, swerved from the fierce flame. Then by Grimhild's magic arts, Sigurd and Gunnar changed shapes and arms, and Sigurd leapt up on Gran's back, and the good steed bore him bravely through the flame.
This poem makes clear some original features of the legend which are obscured elsewhere, especially in the Gudrun set; Grimhild's treachery, and Sigurd's unintentional breach of faith to Brynhild.
And when she heard of the great hoard that was his she had greater wish and will that he should be one with the Nibelungs. She looked on the helmet of gold and on the great armring that he wore, and she made it her heart's purpose that Sigurd should wed with Gudrun, her daughter. But neither Sigurd nor the maiden Gudrun knew of Grimhild's resolve.
This part of the story is summarised in Gripisspa, except that the writer seems unaware that the Wishmaiden who teaches Sigurd "every mystery that men would know" and the princess he betrays are the same: "A king's daughter bright in mail sleeps on the fell; thou shalt hew with thy sharp sword, and cut the mail with Fafni's slayer.... She will teach thee every mystery that men would know, and to speak in every man's tongue.... Thou shalt visit Heimi's dwelling and be the great king's joyous guest.... There is a maid fair to see at Heimi's; men call her Brynhild, Budli's daughter, but the great king Heimi fosters the proud maid.... Heimi's fair foster-daughter will rob thee of all joy; thou shalt sleep no sleep, and judge no cause, and care for no man unless thou see the maiden. ... Ye shall swear all binding oaths but keep few when thou hast been one night Giuki's guest, thou shalt not remember Heimi's brave foster-daughter.... Thou shalt suffer treachery from another and pay the price of Grimhild's plots.