When the actress they cast to perform nude during the ritual in the opening scene and during a flashback later in the film couldn't show up because she was arrested, producer Les Young immediately volunteered his young wife, Moira, who was the associate producer, without consulting her first. When she objected, he convinced her they had no other options and would lose money if the film was delayed while they searched for another actress. She reluctantly agreed. At first, she was only going to be topless, but the day of shooting, Les and director Norman Warren told her it would be better if she were fully nude to give them more options for framing the shot. Moira agreed, but she told Les she wasn't happy about it. Though they had a closed set, she said later it was very embarrassing having to strip all her clothes off and lie on the ritual table stark naked surrounded by male extras and crew for hours while they filmed. To make matters worse, the extras were all wearing masks so she kept imagining all of them were leering at her breasts and vagina. Her breasts and pubic hair then ended up prominently displayed on screen while another nude actress rubbed her hands all over Moira's body. She joked years later that she can't imagine any other producer ever went as far as she did to help a film. She also said she now had more respect for actresses who performed nude because it was tough to do.
It was on this low-budget (£15,000) movie that make-up artist Nick Maley first met actress Gloria Walker (aka Gloria Maley) who he married in 1978. Nick credits trying to clean Gloria up, naked in the bath, after her bloody murder scene with the beginnings of their relationship. "We got to know each other rather well that night." Later Nick and Gloria wrote Inseminoid (1981), also directed by Norman Warren.
The shooting script was titled Evil Heritage. The distributor, Brent Walker, didn't like it because he thought people wouldn't understand what it meant. He chose Satan's Slave, saying it was more self-explanatory and gets straight to the point.
A fair share of the crew worked on deferred salaries.
The main location for the film's shoot, the home of Michael Gough's character, which is located in Pirbright, Surrey, was home to the Baron and Baroness De Veauce at the time of filming.
It came up for sale in the mid 2000's and included the cottage seen in this film. Since filming, a large conservatory has been added to the front of the main house.
The house was described as having 11 Bedrooms, 4 Bathrooms, 7 Reception Rooms, Staff Annexe, Grooms Cottage (the one used as the cottage in Terror (1978), an indoor stable block, all weather arena, several other outbuildings, gardens and grounds (including the woodland used in Terror) and paddocks.
The total area for sale covered 32 1/2 acres. The property was sold by agents Brown and Co for an undisclosed sum, although it was expected to be a seven figure sum.