Continuity mistake: In the scene where Aslan dies, after the White Witch leaves, Aslan has 4 teeth, (2 sharp and 2 flat,) but in the next shot, Aslan only has 2 teeth (2 sharp.) Nobody helping the White Witch ever pulls Aslan's teeth out.
Continuity mistake: The unicorn that Peter is riding in the big battle scene has a horn, then doesn't, then does.
Factual error: The locomotive Bradley Manor has a British Railways number plate on its smokebox door - at least 8 years before Nationalisation. GWR locomotives had their numbers painted on the buffer beam.
Continuity mistake: When the Pevensies enter Narnia, Lucy is seen in several shots with her arms at her side while Peter and Susan are apologizing to her, then her arms are suddenly behind her back to throw a snowball at Peter. She was never seen bending down to collect the snowball and Peter and Susan were surprised when she threw it at him.
Suggested correction: Right before she throws the snowball, she is seen walking up to them, so presumably, she made the snowball off-camera.
Continuity mistake: When Lucy first comes out of the wardrobe, it is snowing, and some small amounts of snow are on her hair, but, in other shots, there is either less or more. It keeps switching.
Revealing mistake: During the final battle a harness is shown on the water buffalo soldier as the main centaur attacks and kills him (the harness is visible as the soldier is hoisted into the air).
Continuity mistake: When being chased by the witch (which turns out to be Santa Claus) across the plain, the shadows change direction between shots, and in the close-ups there is more than one shadow per person.