After spending a night together full of so many ups and downs, Ellie and Riley's bites took away all hope they had of continuing their lifelong friendship. Immediately after declaring she'd sacrifice her role in the Fireflies to stay put with Ellie, Riley accidentally summoned the attackers with her loud music. It was a costly mistake that became even more depressing with an understandable outburst from Ellie that ended with the two making the decision to "lose their minds together," rather than end it with suicide right then and there. If the filmmakers hope to show that they have any credibility to fans of the game, they will absolutely include this quote in the film. Even if the scene isn't shown, Ellie's referral to it while she explains how she got her bite to Joel will be sufficient. It can't be stressed enough how much those few words describe the world of The Last of Us. Whether someone turns into one of the infected or stays a human throughout, they will, in a sense, lose their mind regardless. With the movie, it is possible that showing Riley slowly fading away while Ellie stays sane could help with the scene but it should not be considered a requirement, especially after the original story was able to do without it and remain so enthralling. Some extra backstory could go a long way though.