"The telephone was the star of my next film," writes William Castle in his autobiography Step Right Up! I'm Gonna Scare the Pants Off America as he describes I Saw What You Did, a lightweight thriller about two schoolgirls and a prank phone call that backfires with a vengeance. When the girls whisper "I saw what you did, and I know who you are" to a perfect stranger, little do they know he has just murdered his wife and is now out to silence any witnesses. An aging John Ireland plays the homicidal husband and Joan Crawford has little more than a cameo as an amorous neighbor turned blackmailer. Castle leaves the spook-show gimmicks and high-concept twists out of this thriller, which prefigures the teen scream genre by decades, but he proves to be little better than competent as a suspense director. When one of the girls continues to call the killerback, playing at grown-up with a breathy coo and a come-on air, the film shuffles through uncomfortable territory and emerges with an unaccountably cheery denouement. Castle is more at home as a showman, as his giddy, goofy House on Haunted Hill shows, than as a dime store Hitchcock, but the film does exhibit a little Castle flair, such as an inventive prologue framed in a pair of opening and closing eyes.