Revealing mistake: When the dragon is hatching, a light bulb is visible just behind and to the left of her egg. (00:14:10)
Suggested correction: What appears to be a light bulb in the wide shot is actually a leather strap attached to a larger leather item. This can be seen more easily in the close up shot in the moment after the egg fully breaks.
Revealing mistake: When they show the pile of bodies after the final battle, some of the dead soldiers are wearing modern shoes with rubber soles that would not have been available during the Eragon's time. (01:32:05)