When I was a kid, there was a guy who lived in a creepy old two-story house. He was really into Halloween, and had professional props and effects. I'm talking movie quality! I remember a rain effect that he had one year where if you stood on the front porch, looking at the lawn, it looked like it was raining. But, if you stood on the lawn, looking at the porch, you saw no rain. I've always wondered how he did that.