Many of the scenes were filmed in the same location as the climactic battle in Mission: Impossible 2. Many of the tunnels actually existed on the location, although Tim Ferrier designed further tunnels that were built in the studio.
This was a return for longstanding members of the Farscape crew to Middle Head, in Sydney Harbor. The first season episode "Throne for a Loss" was filmed there.
The visit to Arnnesk, and many of the other concepts in this episode were originally created for the cliffhanger to Season 3, before David Kemper devised the script for "Dog With Two Bones."
The scenes included in the "previously on Farscape" were filmed for insertion in "Crichton Kicks," but there was insufficient time to include them. The producers felt inserting them here was the fastest way of bringing the audience up to speed.
Throughout Jool's appearances in the fourth season, her hair remained red the whole time, rather than changing color from yellow to red to reflect her mood, as it had during the third year.
Oo-Nii was played by Steve Le Marquand, Ben Browder's stunt double during the first year of Farscape. He had to redub certain scenes to reduce his strong Australian accent.
Numerous versions of Oo-Nii were created by Jim Henson's Creature Shop to achieve everything that the script required. More than ten pairs of hands and feet were made.
The weird goat in the scenes with the priests was nicknamed "Goatzilla" by Jim Henson's Creature Shop, and fulfilled a long-standing desire of executive producer David Kemper to see a "star goat" in the series.
Wayne Pygram was actually seriously ill throughout the filming of these episodes, and lost a great deal of weight. He eventually had to eliminate all gluten from his diet before he could recover.
Wayne Pygram suggested to director Rowan Woods that Scorpius be led around like a dog to emphasize the total change in his situation.
If you listen carefully to the song that the Priests are chanting on Arnnesk, it sounds very familiar. It is actually taken from some of the harmonies in the Farscape theme, suitably rearranged by Guy Gross.
The music is broadened by Guy Gross's use of the shakuhachi - a Japanese flute that he previously used to good effect in the score for Season 3's "Eat Me."