The dragon's tooth that Bowen holds in the first fight changes shape twice.
When Bowen is helping to train the resistance, Gilbert is just learning how to shoot a bow and arrow. When he goes for the second shot, the end of the arrow (feathers) is spotted black and white, but the next second, as he brings it up to his ear, it has a white feather instead of the black and white one, and it's still the same shot.
Lee Oakes as young Einon speaks received (ie. "well brought up" but not posh) accented English - given his mother's accent, one assumes this is his natural accent. David Thewlis, as adult Einon, speaks with a strong north country accent. It is unlikely he would have adopted this accent as an adult.
The amount of mud on Kara's face after the villagers have pelted her with fruit.
Brother Gilbert tries to shoot an arrow which has black and white flight feathers then there's a shot of him pulling the bow string back showing the flight feathers are now all white.
The graphic at the beginning gives the year as 984. The tear drop shields did not come to England until 1066 with the Normans.
After Draco is 'shot down' into a lake by Bowen, the water remains unaffected as Draco swims.
At the beginning of the movie, when the king sets fire to the peasant's house, you can actually see the other side of the roof catching fire prematurely.
A tombstone at Avalon wobbles.
Crops and trees unaffected by downdraft of dragon's wings.
During the scenes early in the film when Kara is being held prisoner, you can clearly see Dina Meyer is wearing a very bad wig, indicating these scenes were most likely added during re-shoots.
Young Prince's braces visible when he screams trying to help his father.
In the opening scenes of the old castle ruins, white apartment buildings of the nearby village of Chachtice are momentarily visible.