- Brain in a Jar: Not in the film itself, but one of the "fiend" puppets was displayed at a movie theater during the film's premiere.
- California Doubling: England stands in for Canada.
- Colbert Bump: Although the film is very well-known and respected (enough to have been released through the Criterion Collection), James Rolfe gave it high praise in his Monster Madness series, introducing it to new viewers.James Rolfe: It's good brain-bashing fun.
- Creator Backlash: Zigzagged. Arthur Crabtree wasn't happy to be offered this movie at first; a director of war movies and period dramas, he considered science fiction beneath him and only signed on after screenwriter Herbert J. Leder was blocked from directing because he lacked a UK work permit. This led to a somewhat tense shooting experience as detailed below. Crabtree, however, apparently became proud of Fiend after it was finished and considered it one of his best films.
- DVD Commentary: With Tom Weaver and director Arthur Crabtree on the Criterion DVD.
- Fake American: The American Colonel Butler is played by the Canadian Stanley Maxted.
- Fake Nationality: Canadian Mayor Hawkins is played by the very American James Dyrenforth.
- Hostility on the Set: Arthur Crabtree made his disdain for the material known to his cast and crew throughout filming; at one point, he got into a fight with Marshall Thompson and stormed off the picture, leaving Thompson to direct much of it himself.
- Film historian Michael Brooke writes that this wasn't a one-time occurrence, either. Crabtree had a reputation for being a "difficult" director who, although an experienced cinematographer, struggled to master the finer points of filmmaking and often clashed with his actors. One actress commented that Crabtree often left the actors to direct themselves, though "his photographic background ensured that they always looked good."
Trivia / Fiend Without a Face