Lycra/Latex Wallpaper for haunted houses

Design a room in a "haunted house" with a track crisscrossing the room. On the track a maniquin arm will be attached. Also, make a dock or two for the arm so it can lay in wait in various places. Next make wallpaper made out of lycra or latex and paint it so that it looks like regular wallpaper. Now, put a sensor on the doorways to alert the mech. Arm. When the arm has been activated it will run out on the track beneath the wallpapter making it bulge, looking like a supernatural being is trying to get out. To add a little surprise the arm should only be activated randomly.