We're just three weeks into The Last of Us on HBO, but it's already become clear that the writers aren't afraid to go off-script from the video game's version of events. This latest episode focuses mostly on the relationship between Bill and Frank, characters we never actually see interacting together in the game despite an implied long and somewhat tumultuous history.

Those pieces of the episode are its best bits, but before we experience the elongated flashback of their time together in Lincoln, Massachusetts, a scene between Ellie and Joel confirms a popular fan theory regarding how the outbreak of the cordyceps fungi began.

Ellie asks Joel about how it started, essentially wondering who Patient Zero was, and how it spread so fast. According to Joel, who provides a history lesson for both Ellie and the audience, the cordyceps fungus mutated, and he adds that the best guess is it "got into the food supply."