how does the writer convey the horror of the story's ending?

The ending is pretty creepy. John comes home and tries to open the locked door. The narrator tells him where the key is, and he finds it and enters. He asks her what she is doing as she creeps around. She tells him that she has finally gotten out of the wallpaper despite him and Jennie, and that she has pulled off most of the wallpaper so they cannot put her back. John faints, and the narrator keeps creeping over him as she goes around the room.