Elsa Anderson's Double

Elsa Anderson only meets her double three times in real life. She hears her as a voice and she hears her as music. Sometimes the double is confronting, it's almost as if she knows things that Elsa doesn't know. But I think there's also this thing that if we, any of us, met our double, do they know something that we don't know about ourselves? Or even where does mom hide the chocolates?