How does Harry Potter explain that souls and portraits can talk?

Brother upstairs, do you know what science fiction is? That's all based on science. Harry Potter is a magical novel! This is a legendary story!

That's not a soul, it's a ghost. A ghost is a mark left by a person in the world. Driven by their own magic, they can let the soul move in the original world. They are the choice of cowards after death. They belong neither to the world nor to the underworld. Portrait is another world built by magic, and the characters in it also belong to a kind of imprint, which can move and speak through magic. Harry Potter's world can't be delved into, just look at the story and feel its profound meaning.