Janet Leigh was a good sport, who got a kick out of [Hitchcock’s] off-color limericks, puns, and pranks. The worst jokes on Leigh seemed to come just moments before her most important scenes—and she found most of them terribly funny.
Hitchcock had one running gag involving Leigh and Mrs. Bates—Norman’s mother—as he tested the various mummified skeletons created by the effects department. The director “relished scaring me,” Leigh wrote in her memoir. “He experimented with the mother’s corpse, using me as his gauge. I would return from lunch, open the door to the dressing room, and propped in my chair would be this hideous monstrosity. The horror in my scream registered on his Richter scale, decided his choice of the Madam.”
Hitchcock cared about Leigh (and the character she was playing), a concern reflected in the way he helped her out, even acting from the sidelines, during the protracted car-driving interludes (unusual for a director not at all known for hand-holding or even being willing to discuss a character’s motiviations with an actor). In those scenes Marion wears “a troubled, guilty face,” according to the script, and the director “completely articulated for me what I was thinking,” Leigh recalled. “‘Oh-oh,’ he’d say, ‘there’s your boss. He’s watching you with a funny look.’”
—excerpted from Alfred Hitchcock: A life in Darkness and Light