[3] af grjóti einu ‘from stone alone’: The U redaction appears to be unhappy with the accuracy of this claim, reading af grjóti ok jarni ‘of stone and iron’. Flint needs to be struck with iron or steel to produce sparks to kindle fire, though there is no reason why the riddle should necessarily refer to both; cf. Heiðr 63, Note to [All], about obsidian, a flint-stone.