<P> The episode was inspired by the series one episode, "The Entire History of You", which featured a personal implant that one could use privately to review their memories . For "Crocodile", they considered what the situation would be like if these memories were not private, developing a "cat - and - mouse type drama" that would highlight the importance of memories, and to what lengths one with a secret would go to to hide those memories . </P> <P> The episode was initially conceived as having a male protagonist with Andrea Riseborough reading the script with another part in mind . However, after Riseborough liked the journey of the protagonist and asked if the part could be rewritten as a woman, the script was altered in order to accommodate Riseborough . Both Brooker and executive producer Annabel Jones described the change as interesting, with Jones noting that "How often do you see a mother reduced to this level of desperation?" on television . </P> <P> The episode was shot in Iceland and includes scenes filmed in the Harpa concert hall . Brooker had originally called out for filming in Scotland in his script, but Netflix suggested Iceland as a "more stunning backdrop", according to Brooker . During filming, Iceland had its largest snowfall in forty years, which required them to add one line of dialogue to comment on the change of weather to account for the sudden snow accumulation . </P> <P> In May 2017, a Reddit post unofficially announced the names and directors of the six episodes in series 4 of Black Mirror . The first trailer for the series was released by Netflix on 25 August 2017, and contained the six episode titles . </P>

Where was black mirror season 3 episode 4 filmed