Psycho Anthony Perkins
2. Paramount really, really didn't want to make the film.
Paramount rejected the project, refusing to buy the rights to Bloch's book for the director. Unbowed, he pressed ahead anyway, acquiring the source material for $9,500, and setting James Cavanaugh, a writer on TV series "Alfred Hitchcock Presents," to pen the script. While Hitchcock would eventually reject his draft, finding it "dull," the hire was something of a model for the way he would go about the film; while some of his regular collaborators were on board, including Saul Bass and Bernard Hermann, the director decided to predominately use the crew from his TV series in order to make the film as quickly and cheaply as possible. Once Joseph Stefano (the second writer on board) nailed the script, Hitchcock went back to Paramount, offering to make the film for a fraction of his usual budgets with his small-screen crew. Even then, the studio refused, telling him that all their sound stages were full in the timeframe he wanted to make the picture, despite evidence to the contrary. Frustrated, Hitchcock struck a deal with Universal to shoot on their lot, and financed the $1 million budget entirely through his own Shamley Productions banner, with Paramount eventually begrudgingly agreeing to distribute the film. In exchange, the director waived his usual quarter-of-a-million-dollar fee, in exchange for 60% of the gross. He was understandably nervous as a result -- at one point in post-production, he considered cutting the more button-pushing moments and only releasing the film as an hour-long special episode of "Alfred Hitchcock Presents." But Bernard Hermann's score (which Hitchcock had initially fought with the composer over -- he wanted more of a jazz feel, and for there to be no music over the shower scene) finally convinced him to continue "Psycho" as a feature, and the risk paid off in a huge way: the film would be the biggest hit of his career, and Hitchcock personally made $15 million from its release, roughly equivalent to $150 million today.

3. If they'd stuck to the script, the shower scene would have been a lot messier.
As adaptations go, Stefano's take on Bloch's novel was relatively faithful -- after all, it had been the plot that had attracted Hitchcock to the project in the first place. There were a few changes, however. For instance, Marion (or Mary Crane in the source text: the name was changed after it was discovered that there were two real life Mary Cranes in Phoenix, Arizona) only takes up two chapters of the novel, which opens with Bates, rather than her. One of Stefano's major suggestions was to extend her role, and Leigh was always the first choice, although the tight budget meant that she took the project for a quarter of her usual salary (Eva Marie Saint, Lee Remick, Angie Dickinson, Piper Laurie, Martha Hyer, Hope Lange, Shirley Jones and Lana Turner were all allegedly considered for the role as well). Bates, meanwhile, was a more traditional creep in Bloch's novel, a heavy-drinking, overweight man obsessed with the occult and pornography, but Hitchcock liked the idea of a more handsome, less threatening type, and came up with the idea early on of casting Perkins -- although that lost him Kim Stanley ("The Goddess," "Frances," "The Right Stuff"), his initial choice for Lila Crane, who refused to work with the actor. But perhaps the most notable change came in the famous shower scene, which despite its taboo-pushing violence, could have been even gorier -- in the book, Bates/Mother decapitates Marion, rather than merely stabbing her. Partly thanks to the Production Code, and partly out of sensible taste, Stefano and Hitchcock toned down the violence. Not that it made the scene less disturbing -- Leigh would later admit that she was put off showers permanently, only taking them when she couldn't have a bath. Hitchcock also famously received a letter from a man whose daughter had refused baths after seeing Henri-Georges Clouzot's "Les Diaboliques" (the black-and-white photography of which was a major inspiration for the look of "Psycho," aside from it simply being cheaper), and was now refusing to take showers after "Psycho." The director's droll response? "Send her to the dry cleaners."