In the original script of I Saw What You Did, the part of Amy Nelson, the killer's next door neighbor, was a minor part. The studio decided to expand the role in hopes of attracting a name actress.

Barbara Stanwyck was first offered the part of Amy Nelson but turned it down as she was busy with her TV series Big Valley. Stanwyck had worked with director William Castle previously in The Night Walker (1964).

Joan Crawford worked only four days on I Saw What You Did and was paid $50,000, plus a percentage of the profits. Besides the favorable deal terms, she accepted the part because it kept her in the public eye and was better than most of the scripts she was being offered.

Crawford's 25-year-old adopted daughter Cheryl had wanted to play one of the teen heroines in I Saw What You Did but was too old for the role.

Director William Castle cast Sara Lane and Andi Garrett in the two main roles of Kit and Libby, respectively, while they were still in high school. It was the film debut for both actresses.

During the filming of I Saw What You Did Crawford took nips from her ever present flask of vodka during breaks and it obviously shows in her performance in certain scenes.

Andi Garrett, who plays Libby in the film, was completely intimidated by her scene with Joan and was genuinely terrified when the older actress attacked her, pulling her hair and dragging her to the car in their big dramatic scene.

In his autobiography, William Castle related this tidbit about the making of I Saw What You Did: "In the days of the silent film, to get the cast in the mood before a scene, directors used music - a violinist or pianist would select music to match the mood of the given scene. Using the same principle, I played a record each morning before shooting - a little jingle I had written:
Don't laugh little girl,
Better run for your life,
The man you just talked to
Has murdered his wife.
Just to keep the girls in practice, I allowed them to actually make several crank calls a day from numbers picked at random out of the phone book. To experience the actual results, they improvised the calls, getting a sense of reality which they would later translate to the screen."

When an interviewer asked Joan why she was making I Saw What You Did, she replied, "Because I think the film will have a terrific identity with parents and audiences." George Cukor, who had known Joan for years and directed her in numerous films at MGM, later said, "Of course she rationalized what she did. Joan even lied to herself. She would write to me about these pictures, actually believing that they were quality scripts. You could never tell her they were garbage. She was a star, and this was her next picture. She had to keep working, as did Bette [Davis]. The two of them spawned a regrettable cycle in motion pictures."

Famous for his promotional gimmicks, Castle had very specific ideas about the marketing of I Saw What You Did: "Tying up with telephone companies around the country and having huge plastic phones in front of each theatre advertising the picture seemed good showmanship at the time. But the gimmick backfired and the wrath of the phone company descended upon me full blast. A phone number placed in the newspapers around the country asked people to call for a special message. Upon dialing, a girl's voice answered and whispered sexily, "I saw what you did and I know who you are," and then made a date to meet the potential customer at whatever local theatre was showing the picture. The whole gimmick would have worked beautifully, except the teen-agers of America took the "phone game" seriously...It seemed that almost every teen-ager in the country was on the phone, making crank calls by the thousands, jamming the phone lines. In retaliation, the telephone company would not allow us to advertise any further phone numbers and also took away the huge plastic phones in front of the theatres. They even threatened to disconnect my home telephone, and when I called to apologize, they hung up on me."

Castle even had a backup promotional gimmick for I Saw What You Did: "To guarantee safety for the patrons of I Saw What You Did, I devised...a special shock section in the theatres, where audiences could avail themselves of seat belts, much like those in airplanes, so they would stay in their seats during shocks."

by Jeff Stafford

Sources:
Step Right Up! I'm Gonna Scare the Pants Off America: Memoirs of a B-Movie Mogul by William Castle
Joan Crawford: Hollywood Martyr by David Bret
Joan Crawford: The Essential Biography by Lawrence J. Quirk and William Schoell
Bette and Joan: The Divine Feud by Shaun Considine