It's supposed to be a depiction of the devil, or just the presence of evil.
It's the same bald-headed lady that was talking in the garden when Christ was praying at the beginning. The same one towards the end (after the crucifixion) that is in "empty hell" screaming out in anger.
If you got it on DVD, watch the extras. It'll explain more on this.
Thank you kindly, please pull forward.
