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.