use Idyllwild instead, as it was less populated at the time, and was in close proximity to Los Angeles. Bostwick recalled that the filming locations were "In the mountains above Palm Springs, around the USC Music camp. Principal photography began in Idyllwild on in the fall of 1979, with a budget of approximately $150,000. The film was shot over the course of ten days, with filming occurring Monday through Friday between October 15 and October 29. The film was shot on 35mm with a Panaflex camera by cinematographer João Fernandes, who was credited under the pseudonym "Teru Hayashi." Additional photography of the wildlife close-ups was completed by Gary Gero. Edwin Brown incorporated the various footage of animals as an "analogy" to the relationship between predator and prey, which applies to both animals and humans, though he conceded that some of the nature footage was added to increase the film's running time. Brown estimated that around 70 percent of the nature footage in the film was stock footage, while 30 percent was filmed by Fernandes and Gero. He has stated that, due to budgetary restrictions and running out of film stock, some sequences in the screenplay went uncompleted, including one in which Mark, the forest ranger, joins the campers at their campfire. Producer Summer Brown spent a significant amount of time on set, and Thureson recalled her as being a "mother hen" figure to the cast and crew. Much of the dialogue between the characters was improvised, specifically during their hiking scenes. While the majority of the film was shot in Idyllwild, some sequences were filmed elsewhere: Coogan's scenes in the forest ranger station were shot on a studio set, while the sequence featuring Bostwick playing banjo was an insert shot filmed in Lake Mead, Nevada. Additional pickup shots were completed in Los Angeles in early 1980, including the final shot of the cave, which was filmed at the Bronson Caves in Griffith Park. Special effects John Carl Buechler served as a special effects designer on the film. Struycken recalled undergoing an elaborate latex makeup application to achieve his character's deformed appearance. Music The film's score was composed by Don Peake, who had also composed the score of The Hills Have Eyes (1977). Director Edwin Brown was an acquaintance of that film's producer, Peter Locke, and was put in contact with Peake to write a musical score. Producer Summer Brown stated