The Spike Walls (also called Thorn Walls) are un-catch-able objects that appear in Luigi's Mansion. They appear in some rooms after Luigi enters a room. They make Luigi not able to exit the room until the lights come on. They are gray, but the kinds that block the areas have an electric flash around the door. They appear and disappear with a "puff of smoke". Oddly, they do not hurt Luigi if he touches it. To open a door with spikes on it, you will need to obtain a boss key after winning a boss battle.