At the beginning of Hrafnsmál the Valkyrie calls the raven "the skull picker of Hymir":
1. Hearken, noblemen, while I celebrate Harold the magnificent and his feats of arms. I will tell of the words which I heard spoken by a maiden fair and golden haired as she held converse with a raven.
2. The valkyrie prided herself on her wisdom ; — and the warlike maid took no pleasure in men, for she knew the language of birds. With white throat and sparkling eyes she greeted the skull picker of Hymir as he sat on a jutting ledge of rock,
3. 'How is it with you, ye ravens? Whence are ye come with bloody beak at the dawning of day? Torn flesh is hanging from your talons, and a reek of carrion comes from your mouths. I doubt not that ye have passed the night amid a scene of carnage.'
Source: Anglo-Saxon and Norse Poems. Edited and translated by N. Kershaw.
Is this a reference to the giant Hymir (and his unusually hard skull)?