Naura Hayden originally was slated to play Lise. However, she quit the project when she discovered that she would only receive second billing.
Although it was shot in Denmark, producer Sidney W. Pink had the dialog spoken in English. When the finished film was turned over to American International, Pink was informed that the dialog would be re-looped. AIP head Samuel Z. Arkoff felt that what he called the "sing-song Scandinavian accents" would have U.S. audiences laughing. Pink objected and threatened to file suit. After Pink had other industry professionals view his version of the film, the lawsuit was dropped and AIP released the film in an edited and re-dubbed version.
Because Dirch Passer was hugely popular as a comedic actor at the time this was filmed, the producers at one point were going to call the film "Dirch and the Dragon".
Denmark's first and only "Monster" movie.
Footage from this movie was used in the American animation-show South Park in episode #704: "Cancelled".
Many of the elements in the script for this film were originally intended for the aborted "Volcano Monsters" project, also written by Ib Melchior.
Two versions were filmed: One was the original Danish version, and the other was filmed with the actors speaking English. All actors were in both versions, except for actress Bodil Miller, who was unable to speak English. Her character of Connie Miller was played in the English-speaking version by Marlies Behrens. American International Pictures used the English version for the US release, and not only heavily edited it, but dubbed over the Danish actors.