Bugge proposed that the -toskr element is a reformation of the Old English word tūsc (Old Frisian tusk) and, in turn, that the element Rata- represents Old English ræt ("rat").
In both the Poetic Edda and the Prose Edda, the squirrel Ratatoskr carries messages between the unnamed eagle and Nidhöggr, the wyrm that resides below the world tree.