The last screen appearance for Dave Brockie, the singer of the metal band GWAR. Brockie was a regular on Adam Green's TV show Holliston (2012), as well as a close friend. There was discussion of cutting Brockie's scene (in which he prophetically declared, "I have been a monster, I will always be a monster and after I'm dead, I will be a dead monster!") but it was ultimately decided that it would be retained since it was the last footage of Brockie that was ever shot.
Adam Green's wife Rileah Vanderbilt appears as herself throughout the film, which was in production for nearly five years. By the time the movie was finally released, they were divorced.
The idea for Digging Up The Marrow spawned in 2010 when Green received a fan letter from a Hatchet fan claiming that the fan could prove that Green's fictitious character "Victor Crowley" was in fact real. Much like the fan mail package from "William Dekker" depicted in the film, the Hatchet fan letter contained pictures, maps, and other manufactured evidence that the fan claimed proved "Crowley's" existence. Not wanting to get involved with a fan who may potentially be insane and not wanting to do a "Crowley" project outside of Hatchet, Green discarded the fan's package but started thinking of a docu-style story where he receives a similar kind of package from a fan claiming that monsters are real and then embarks on a journey to see if the fan can prove his/her claims. Just a few weeks later, artist Alex Pardee approached Green at a convention with a pamphlet for his most recent art exhibit called "Digging Up The Marrow" where the story line followed a mysterious man named "William Dekker" who claimed to have discovered where monsters actually live. After reviewing Alex's concept and his incredibly original monster designs, Green contacted the artist and discussed combining their ideas to make a movie.
During the edit suite scene where Adam Green and Will Barratt come up with the idea of traveling to Boston to speak to someone at the police department where Dekker claims to have once worked, a monster named "Tombstone" can be seen on the monitor behind Adam Green and Josh Ethier. The creature is camouflaged as one of the cemetery head stones but slowly stands up at one point and walks out of the cemetery unseen by Green, Barratt, or Ethier. Many audience members miss this and other purposely subtle hidden moments in the film but have slowly begun to discover them upon repeat viewings. The film was designed to offer new surprises whenever audiences re-watch it and look more closely. "Tombstone" can be seen up close in the accompanying 30-minute documentary "Monsters of the Marrow" included on the US DVD and BLU-RAY release of the film.
Almost no CGI was used in the film, to help ensure the artist renderings of the monsters, done by Alex Pardee, were kept true to form.