Cinematographer Vincent Monton said that the weather conditions while shooting the film were eerily co-operative. He said when the script would call for a scene with sunny skies the weather would be beautiful, but as the intensity and strangeness of the script grew the weather conditions would change to match the moody atmosphere of the scenes being filmed. Throughout the shoot the weather always seemed to change to suit the scene that was being made!
The decision to have rainy weather in the early driving scenes was an effort to hide the fact that the interior scenes in Peter's jeep were filmed inside a darkened garage. During the shooting grips would run past carrying flashlights to make it appear like they were lights from passing cars.
The mysterious shadow near Peter (John Hargreaves) in the ocean was actually made by a crude structure of trash bags that was being pushed along through the water by Richard Brennen, who was submerged just beneath it.
The tree that the harpoon gets impaled into, then later dies and decays throughout the climax, wasn't actually part of the forest at the filming location. It was cut and transported to the location for the shoot so that it could gradually be destroyed during the film.
When the film was screened at the Cannes Film Festival, producer Richard Brennen noticed a man get up and leave the screening after only 10 minutes of the film. He followed the man out to ask him why he was leaving. It turned out the gentleman was a film distributor for South America and was going to buy the rights to the film after seeing only minutes of it. In total four foreign distributors bought rights to release the picture during the screening.
Even though star Briony Behets was married to director Colin Eggleston at the time, Behets wasn't Eggleston's first choice to play the co-lead role of Marcia. Behets only got the role later after the other actress' casting fell through.
Though filming of this Australian movie was completed in May 1977, its theatrical release was delayed, and the film was not widely released theatrically in Australia for almost two years, launching 29 March 1979.
According to this film's DVD Audio Commentary, the dead kangaroo on the road seen in this movie was a real dead kangaroo, the animal was already deceased prior to its transport to the shoot and its subsequent brief appearance.
This movie was a failure at the box-office in Australian. It was also not nominated for any Australian Film Institute (AFI) Awards in a very competitive year. However, the film fared better critically and commercially outside of Australia and won some awards at some film festivals, mainly ones that specialized in the fantasy/science-fiction/horror genres.
According to the DVD Audio Commentary, this film's lead actor John Hargreaves is buried with the Medalla Sitges en Plata de Ley Actor's Award that he won for this film from the Sitges - Catalonian International Film Festival.
Because not all the animals that could be photographed were found in the Bournda State Reserve and the surrounding Bega environs in New South Wales, some second unit photography was done in Tasmania for filming of such non-mainland Australian fauna such as the Tasmanian Devil.
The book read by Marcia while she is in the tent is 1955s "The Inheritors," by William Golding (better known for Lord of the Flies). The book keeps with the theme of the movie by telling the story of one of the last bands of Neanderthals as they are being systematically wiped out by a more advanced tribe of Homo sapiens.
The trivia item below may give away important plot points.
No direct explanation, only hints, are given as to why the mysterious events within nature occur, typical of the man versus nature supernatural horror movie. This film continues this tradition in this sub-genre of films of which Alfred Hitchcock's The Birds (1963) is considered the first and lead example.