Lately, I’ve been thinking a lot about horror. For the next meeting of my screenwriting group I’ve agreed to discuss the horror genre, and show a classic horror film. Since this is for the purposes of writing, I picked a film that would be well-known by everyone, had a script online that everyone could read in advance, and I decided that I’d go with a movie that was not based on previous material (book, comic, short story, etc.). If we’re trying to flex our writing muscles to generate new concepts I figured we might as well look at how an original idea was developed for the screen. So, I chose…