The object records of the four rocks (the types 2C to 2F). Set_Up_Room_Objects copies one of them, chosen by the room x, into a decoration record, and then writes the x position that it takes from the table at Room_Object_X_Positions. The y position A0 is the floor. Bytes 0A to 0E give the size of the rock as an obstacle, so that creatures and weapons bounce off it: its half width, the width of its middle, its height, its depth and the x offset of its middle (see Check_Object_Contact). Bit 0 of the redraw flags is set so that the rock is drawn without being erased first.