Visible crew/equipment: In a scene in a cave that is the lair of the "eaters of the dead," the camera takes an overhead wide angle shot of the "eaters" walking down into the cave. It is possible to see a young man wearing a burgundy t-shirt and beige shorts (a crew member), sitting against the wall of the cave cross-legged. (01:16:55)
Suggested correction: I've watched this scene a number of times on YouTube and I'm certain that this "crew member" is an extra. He is not wearing a T-shirt and shorts, his clothing is correct for an extra. There are also other extras sat cross-legged a few feet from him.
Factual error: The Vikings follow the Norse religion, and make several references to it throughout the movie. But when waiting for the first Wendol attack, Herger states "The All-Father wove the skein of your life a long time ago". In Norse mythology, the All-Father (Odin) did not weave the skein of life, the Norns did.
Suggested correction: The movie takes place in the 900s AD, and Norse myth wasn't put in writing until centuries later with the Prose Edda in 1220. Prior to that, it was spread through oral tradition; who's to say the details didn't change/update in the retelling over the next couple of centuries?