Shel's phone-call (in Swedish) was entirely improvised by MyAnna Buring. The filmmakers had no idea what she said until much later.
The rainbow featured prominently in the film is a real one. There was a rainbow written into another scene, but it was changed when the crew saw one during the shooting of the scene.
The scene where Jay rips off the table cloth was taken from several episodes in writer Amy Jump's childhood.
When Jay and Gal are running in the tunnels, the shark equivalent of whale song is played on the soundtrack.
Jay (Neil Maskell) and Gal (Michael Smiley) investigate the storage locker filled with porn and briefly watch something horrible on the video screen. It's never stated what they're seeing, but "Smiley's imagination was so active in this scene he said he almost threw up into his own mouth."