Roberta Frank reviewed the historical evidence for the rite in her "Viking Atrocity and Skaldic Verse: The Rite of the Blood-Eagle", where she writes: "By the beginning of the nineteenth century, the various saga motifs—eagle sketch, rib division, lung surgery, and 'saline stimulant'—were combined in inventive sequences designed for maximum horror." She concludes that the authors of the sagas misunderstood alliterative kennings that alluded to leaving one's foes face down on the battlefield, their backs torn as carrion by scavenging birds. She compared the lurid details of the blood eagle to Christian martyrdom tracts, such as that relating the tortures of Saint Sebastian, shot so full of arrows that his ribs and internal organs were exposed. She suggests that these tales of martyrdom inspired further exaggeration of the misunderstood skaldic verses into a grandiose torture and death rite with no actual historic basis. David Horspool in his book "King Alfred: Burnt Cakes and Other Legends", while not committing to the historical veracity of the rite, also saw parallels to martyrdom tracts. Frank's paper sparked a "lively debate".