The blood eagle as a Viking method of executing a person, may be the result of mistranslations and not historically accurate.
The execution method of the blood eagle in which victims were sliced open along the spine, had their ribs snapped open so it would look like wings, the lungs pulled out and salt poured in, may be a mistranslation of the Icelandic poet Sigvat Thordarson’s famous poem – Knútsdrápa. The poem is about Ragnar Hair-Breeches’s sons slaying King Ella of Northumbria in revenge. The stanza in question has been translated as both “Ivar caused the eagle to cut the back of Ella” and “Ivar cut the eagle on the back of Ella.” However, only the first translation makes literary and historical sense, as it fits in with the unique structure of the Icelandic poetry as well as the tradition of describing a slaughter as providing carrion for birds. The second translation led to a 14th-century interpretation that still exists today of the Vikings enacting a particularly horrid form of retribution.
This dreadful description of one of the methods used by the Vikings to kill a person, lasted to our days as the correct form of translation in an attempt to mark the Vikings as the barbarian bloodthirsty hordes the priests and monks believed them to be. The victims of the Vikings gave them a terrible reputation and later on the historical documentations writen about them which have survived to our days, were made centuries later when the Vikings were no more and the truth about such events had been altered from writer to writer.