Oh man this scene haunted me when I was 8 or 9. A couple years ago I convinced my wife to watch this movie, and I eagerly waited to see her reaction to this scene. And when it finally happened, nothing. No reaction at all. I asked her, "wasn't that scary?" And she replied, "That?! That was the worst costume I've ever seen."
It was all the build up to that point. The fields, the dogs, the encounters where the characters never actually see them. The denial, trying to convince themselves it's nothing. Animals, or prankster neighbors. Then in an instant, all their worst fears are true.