In 1958, the Daily Telegraph was so horrified by what they saw onscreen that they suggested the BBFC create a special new category for the film - "For Sadists Only".
According to Peter Cushing in his memoirs, the chimpanzee that was used for the film took a liking to the actor. Every morning before work, she would greet the actor with a kiss.
According to co-star Francis Matthews, the brain that was used for the laboratory scenes was taken from a sheep. Unfortunately, someone on the set forgot to store the brain in a fridge overnight and the smell the next morning was horrendous.
Several sets from "Horror of Dracula," which was filmed immediately before "Revenge of Frankenstein," were reused.
In the finished film, Dr. Stein says nothing as the monster approaches, calling him "Frankenstein." In the trailer an alternate take was used in which Stein calls out "Karl! Karl!" It was decided that this would only implicate the doctor more and the silent take was used instead.