David Cronenberg laments not having the benefit of CGI to make the slug look better or at least erase the wires, but he is okay with it as a product of its time. "Unlike George Lucas I had no desire to go back and correct it with modern technology. Let it live in the time that it existed with all the flaws. That's where it belongs."
David Cronenberg has mentioned that he believes screenwriter Dan O'Bannon borrowed heavily from the creatures in this movie for his own movie, Alien (1979). Cronenberg stated, "I have to say that some of my images like this [parasite] ended up in things like Alien, which was more popular than any of the films I've ever made. But the writer of Alien has definitely seen these movies, Dan O'Bannon. The idea of parasites that burst out of your body and uses a fluid and leaps on your face, that's all in Shivers." As recently as a 2015 Collider interview, Cronenberg mentioned how Alien "totally ripped off things from my movie Shivers..."
Susan Petrie was unable to cry, so David Cronenberg used onions to help her produce tears. It worked, but the camera was out of focus when the scene was shot. Cronenberg was out of onions, so Petrie agreed to let him to slap her on the face. He slapped her until her face went numb. Barbara Steele, the other actress in the scene, was not informed, and thought David had been beating her. After the last take was finished, she angrily confronted Cronenberg, holding him off the ground by his collar as she shouted at him, threatening to beat him up. Scared, Cronenberg told her what really went on. Once the other actress confirmed the story, they had a good laugh.
Canadian journalist Robert Fulford attacked the movie in the magazine "Saturday Night." Since it was partially financed by the National Film Board of Canada (NFB/ONF), Fulford headlined the article "You Should Know How Bad this Movie Is: You Paid for It." David Cronenberg said the article not only made it more difficult to obtain funding for his subsequent movies, it got him kicked out of his Toronto apartment.
David Cronenberg cast Lynn Lowry as Nurse Forsythe because of her haunting eyes and strange screen presence.