Geisterdamen appear to be albinos. Their eyesight is not so hot; cave dwellers, used to the dark. The lack of pupils in their eyes supports this. They hear well though. When we first meet them they have come to explore what sounded like a familiar voice, only to discover "actors" . What attracted Etaoin and Sherdlu to Agatha and Lars? Most likely the sound of Agatha doing Lucrezia, their Goddess, in the play dialogue. If they inspected things based on sight then they would have checked out other parts of the circus also. As cave dwellers I wonder if they refer to the world of sunlight as the "Shadow World" since there would be no shadows in the dark.