To create the roar of the monster, Sound Supervisor Jeffrey L. Sandler asked his son Robert Sandler to come up with something scary. The monster's roar was a dog & cat fight, played backward, and slowed down. And to test it's effectiveness, speakers were set up at the ends of 4 long hallways at Glen Glenn Sound in Burbank,Ca. With the lights out, Jeffrey and Robert played the effect...they were both too scared to walk down the hall alone to turn the lights back on.
Some believe that "The Boogens" is an actual term once used by miners to describe the fear some would experience while spending too much time in deep mines. In fact, it was a word fabricated by screenwriter David O'Malley, using the word "boogeyman" as it's root.
Co-writer David O'Malley based the script on things that scared him. For example, the sequence in the garage was inspired by O'Malley's fear of being attacked by rattlesnakes in the garage of his home.