Let me know what you all think....
I'm 99% sure I saw the lamp post as having only one arm in the film. Film stills I've dug up on the web also seem to show it as one-armed.
I think the arm of the lamp post that Jadis yanked in London and threw at Aslan in Narnia grew into what it came from....which was (now) a one-armed lamp post.
I find that detail so delicious!
Edited to bump up in hopes of discussion!