Alfred Hitchcock didn't like to use sleight-of-hand to mislead viewers, but he did so in perhaps his most famous scene—the shower murder in Psycho, writes Steve North in Salon. (And if spoiler alerts apply after 50 years, here it is.) That's not Tony Perkins in drag wielding the knife. Hitchcock used a noticeably larger extra because he was afraid Perkins' slight frame would be too easy to recognize in silhouette—and thus people would know all about Norman Bates only a half-hour into the film.
How does North know? He recounts an interview with Perkins himself. (Which means this isn't exactly a newly revealed secret, but the article is still fun.) "Hitchcock was very worried that the dual role and nature of Norman Bates would be exposed if I were to appear in that scene," Perkins told him. "He was outspokenly eager to not play any tricks on the audience in his films, to do anything that couldn’t be thought of as fair play, but in that instance, he in fact did." (More Psycho stories.)