As I said in the user comment I wrote a couple of weeks ago, I did not care much for the slasher movie "The Mutilator" - it had some good gore, yes, but that's about all. However, the making of the movie documentary that comes as a supplement with the Blu-ray release of the movie is much better. It's true that even though the documentary is of significant length (75 minutes long), there are all the same some key details about the production that are kind of vague or are not mentioned at all. But the documentary does all the same prove to be informative. You learn about the various pitfalls and struggles that can happen in the making of a B movie. Equally interesting is meeting key people in the production of the movie and learning what they dealt with, what they thought at the time, and what they think now. (And they all come across as very nice people you wouldn't mind meeting, even if you don't care about their movie or horror B movies in general.) This is a well done documentary, and it will make you wish that more B movies released on Blu-ray or DVD would have documentaries this substantial.
