After viewing the beheading-scene for the first time, actor Abdilamit Sabani was visibly disturbed by the realistic nature of the sequence, and asked not to see it again.
The basement-sequence was filmed in a basement which was shared by the 7-Eleven that was used for filming, and a pastry shop. The proprietor of the 7-Eleven forgot to inform the pastry shop about a movie-shoot down in the cellars, and their cleaning lady almost panicked when she stumbled on the results of special effects artist Mirja Anette Eriksen, believing to have witnessed a real murder. Director Frode Graadahl quickly approached her and informed her about the film-shoot before things got out of hand.
This was actor Egzon Neziri's first film, and he used to get nervous when arriving on set. Frode Graadahl told him to mimic the infamous "chest-thump/humming"-chant used by Matthew McConaughey in The Wolf of Wall Street (2013) to help him calm down before takes.
Cinematographer Robert Egron Erstad called director Frode Graadahl on the morning of the first day of shooting, informing him that he was stuck at the airport in São Paulo, Brazil. He got Thomas Bjørnstad to cover for him until he got back to Norway.
Actress Mette Holt was originally offered the part of The Doctor back in 2011, but was unable to come to Norway for filming at the time. The shoot was severely postponed, and this gave director Frode Graadahl the opportunity to later offer Mette Holt her the part of The Negotiator, since he'd already casted Elise Christine Eide as the doctor in the meantime. Mette Holt read the script and called Graadahl to talk about the part and said "she's like a negotiator" which Graadahl liked so much that he decided to refer to the character as such from then on.