In the excerpt you provided from "The Open Window," the setting of the room momentarily shifts in the way it "seems to become less creepy and more dynamic" when the aunt enters.
This is because Framton Nuttel feels a sense of unease and anxiety before the aunt arrives, primarily influenced by the niece's intriguing yet unsettling conversation. However, when the aunt enters the scene, her presence brings a different energy to the room. Her demeanor and conversations help to alleviate some of Nuttel’s tension, making the atmosphere feel more animated and less eerie.
So the correct response is: It seems to become less creepy and more dynamic. This shift reflects the change in the social dynamic and the emotional tone of the interaction once the aunt is present.