What's the One Halloween Decoration That Can Instantly Make a House Look Spooky?

Sometimes, one simple Halloween decoration is all it takes to turn an ordinary house into something straight out of a horror movie. It could be fake spider webs, creepy skeletons, glowing pumpkins, or even a few well-placed tombstones in the yard. What's the one Halloween decoration you think instantly makes a house look spooky, even without all the extra decorations?