The producers originally planned to have creatures called voles in the film as well as the slime people. The voles would have been wolf-like animals from underground that had been domesticated by the slime people, but the were left out of the final script.
The scenes of devastation supposedly caused by the fight with the slime people (shown briefly while the group is driving away from the airport) is actually footage of the Hollywood hills shortly after a wildfire swept through the area.
The scenes in the butcher shop and freezer were filmed in an actual butcher shop owned by the father-in-law of actor Robert Hutton in Lancaster, California.
In an interview, star/director Robert Hutton said that neither he nor the stuntmen were ever paid for their work in this film.
Blair Robertson, who was one of the scriptwriters, plays Mrs. Steel in the TV news footage.
The only film directed by Robert Hutton, who continued acting in England, where he wrote the script for Persecution (1974), starring Lana Turner (because he didn't like cats).
Susan Hart didn't have to read for the role of Bonnie Galbraith; she was automatically cast on the basis of her attractive looks alone when she showed up for the casting session.
Because of this film's low budget, Susan Hart was given only $35 to buy her own wardrobe.
The two bums who appear in the theater are played by Joseph F. Robertson and Edward Finch Abrams, the film's producer and associate producer, respectively.
According to director Robert Hutton in a 1989 interview, designing and making the slime people costumes consumed over half the film's entire budget.
Richard Arlen was originally considered for the role of Prof. Galbraith.