You know how realistic that horse head in The Godfather looks and how terrified the actor appears to be when he sees it in bed with him? Well, that's because the head was actually a real horse head -not a prop. The design team actually tried to make a prop horse head, but Francis Ford Coppola didn't think it looked quite real enough, so instead they bought one from a dog food factory.
Over on TopTenz, you can read about ten movie props that were actually real -including the flame thrower guitar in Mad Max, the skeletons in Poltergeist and the door Jack Nicholson chops down in The Shining.