The scariest thing I've ever seen was a play put on by some 15 year olds at my old school (I was visiting as a former head girl). They did the story of Lizzie Borden and the acting was superb and the atmosphere they created was downright terrifying. And at the end they did this layered chanting thing from different corners of the hall just going "Lizzie Borden took an axe and gave her father 40 whacks, and when she saw what she had done, she gave her mother 41" over and over again adding more voices and getting louder every time. And at the very end they somehow did this subliminal flicker thing where they just flashed red light on the stage and there were the three characters just standing there... I still get the jitters now just thinking about it!