What did Alberto accidentally call Sophie?

Alberto accidentally refers to Sophie as Hilde.

In "Sophie's World" by Jostein Gaarder, there is a scene where Alberto accidentally calls Sophie "Hilde" during a philosophical discussion. This moment is significant because it hints at a deeper layer of the story and raises questions about the nature of reality and the characters' identities. It foreshadows the revelation that Sophie's world is a creation in a philosophical narrative written by Major Albert Knag for his daughter, Hilde Møller Knag, blurring the lines between fiction and reality in the book.