The giant born from Ymir’s feet had six heads.
This unusual birth appears in the poem Vafþrúðnismál, where Odin asks the giant Vafþrúðnir how Ymir produced offspring without a female partner. The answer describes a male and female emerging from Ymir’s armpits, while his feet together produced a six-headed jötunn.
The detail is easy to misremember because Ymir himself is the central primordial giant, but the six heads belong to the separate being generated by his legs. Norse myth often gives primeval beings strange reproductive powers: Ymir also sweats a male and female from his body, beginning the line of giants.
Ymir is known in related traditions as Aurgelmir and is treated as the ancestor of the jötnar. Later, Odin, Vili, and Vé kill him and construct the cosmos from his remains. His flesh becomes earth, his blood the sea, and his skull the heavens, which the four directional dwarfs support.