Early on Sunday's episode, Ellie asks Joel how the cordyceps infection spread so quickly back in the day. Who was the first person bitten? Joel tells her the best guess is that the cordyceps mutated by getting into the food supply and a basic ingredient like flour or sugar.There were certain brands of food that were sold everywhere, Joel tells Ellie. All across the country, across the world. Bread, cereal, pancake mix. You eat enough of it, it'll get you infected.When Joel mentions pancake mix, it should make you think back to the show's first episode. Sarah originally wanted to make pancakes for Joel's birthday. They were out of mix, so they had eggs instead. If they had pancakes for breakfast, they likely would've been infected.Joel and Sarah avoided possible infection multiple times on the premiere. When they left the house, their neighbor offered them biscuits. The older neighbor eating one later became infected. Sarah also avoided some cookies in the afternoon because she wasn't a fan of the flavor.You can read more on the their near miss here.Bill's Lincoln, Massachusetts, sanctuary looks like a pristine, well-preserved town that's frozen in time and unmarred by the apocalypse.The one featured in the game isn't the sort of place you'd want to make your home for two decades. It's falling apart, grimy, and looks like a looted town. Joel, Ellie, and Bill still run into the infected in Bill's safe space.In the game, Bill leads Joel and Ellie through a church where he sleeps on a beat-up mattress in a mostly empty room.Bill lives like a king on the show in a house with a white-picket fence. There is a church in Bill's town, likely a nod to the one featured in the game.Sunday's episode is a complete expansion on Bill and Frank's game characters. The pair's love story on HBO's adaptation is a much richer and respectful adaptation of Bill than the version that's glossed over in the game where his sexuality is merely implied, but never directly stated, and the relationship is depicted in a negative light.In the game, Joel and Ellie seek out Bill, shown as a paranoid loner who speaks to himself, to help them fix a vehicle and carry on their mission. Frank, also Bill's partner in the game, is only seen dead, hanging after committing suicide some time ago after an infected bit him. In the game, we learn the two had a nasty falling out, resulting in Frank's eventual death. As far as we know in the game universe, Bill is still alive. During a Zoom conversation with showrunners Craig Mazin and Neil Druckmann in December, Insider asked why the show expanded upon Bill's story in a significant way, giving him a happily ever after.Mazin said that after two episodes filled with action and danger, there was an opportunity to take a breath in the story and show survival from a different vantage point.There's this lovely thread that indicated this hint of a relationship between Bill and Frank in the game, Mazin said.He added: I just suggested to Neil that maybe we pull that thread and we take it in a different direction in terms of the way it was depicted in the game, and use it to show the passage of time and use it to explore some of these themes that are so important to the length of the show, themes about what it means to love somebody, the different kinds of love, including a love that can be very protective and violent and dangerous, and how we could give these two men a win.You can watch our conversation with the showrunners on Sunday's episode here.On Sunday's episode, we see Joel and Tess visit with Bill and Frank in the past.In the game, Joel and Tess only know Bill. Frank was his secret partner. When Bill, Joel, and Ellie come across Frank's body, a confused Joel asks Bill about the man.Towards the episode's end, Frank is seen on a wheelchair and has limited use of his hands and legs. On HBO's official TLOU podcast, host Troy Baker asked the showrunners Frank's diagnosis.We didn't necessarily want to specify it for the audience, Mazin said. It was either MS or early ALS.Bill cooks Frank rabbit and serves it with a the Beaujolais wine.The shot of Bill walking out of the kitchen into the dining room is a match of the same scene from earlier in the episode when he serves a hungry Frank food.Bill's letter to Joel provided hope and advice for him to take care of Tess.It read: ...I respect you so I'm gonna tell you something because you're probably the only person who will understand. I used to hate the world and I was happy when everyone died. But I was wrong because there was one person worth saving. That's what I did. I saved him. Then, I protected him. That's why men like you and me are here. We have a job to do and God help any motherfuckers who stand in our way. I leave you all of my weapons and equipment. Use them to keep Tess safe.Since Bill doesn't die in the game, there's no note from him for Joel to find. Instead, players can find a mean-spirited note in the game addressed to Bill from Frank. If you find it, Joel hands it to Bill who reads it and drops it to the ground.In part, Frank's note to Bill read: I want you to know I hated your guts. I grew tired of this shitty town and of your set-in-your-ways attitude. I wanted more from life than this and you could never get that.Not only did Bill and Frank live in a well-kept town on the show, but Bill did eventually understand what Frank wanted from life. The two built a beautiful life together despite the circumstances of the apocalypse.Bill's letter told Joel he's still here to keep people, like Tess, safe.Druckmann told Insider the lesson Bill learned about what's important in this life on Sunday's episode reflects back to Joel and his current mission to get Ellie to the Fireflies. He may not be able to protect Tess, who died on last week's episode, anymore, but he can use his abilities to help a young teenager.Of Bill's letter to Joel, Druckmann said, He gives him this warning that's too late. Here's what you gotta do for Tess. And then Joel realizes, 'Well, it's too late for Tess. Maybe it's not too late for this kid.'After making a car battery with Bill's supplies, Joel opens up to Ellie for the first time and tells her about his brother Tommy, who's located in Wyoming and in trouble.Joel and Ellie leave Bill and Frank's town in Bill's blue-and-white pick-up truck on the show.Bill leaves Joel the car key on the show. The truck is similar to the one Joel and Ellie eventually drive off with in the game, but it's found in a different way.In the game, Ellie and Joel go on a hunt for a car battery with Bill to patch up a vehicle to continue on their journey west. Instead, the trio come across Frank's body before Ellie finds the car battery they were searching for in a blue-and-white truck. After a fallout with Bill, Frank found Bill's hidden car battery and planned to use the truck to escape the town before he was bitten and infected.Ellie finds a cassette tape in the glove compartment of the truck. It's Linda Ronstadt's Long Long Time.That's the song Bill and Frank played on the piano the first day they met. Instead of making a meal for Frank and allowing him to hit the road, the two shared an instant attraction, fell in love, and spent their lives together for 16 years.The episode closes with the song playing as the camera pulls into Bill and Frank's open window where they're presumably lying dead in each other's arms as we hear the lyrics: I think I'm gonna love you for a long, long time.On HBO's official podcast for the series, Mazin said the song was used to bring Bill and Frank together. We had this idea that Bill and Frank would connect over a song, that would be the thing that would essentially lead Frank to feel differently about Bill, to not just go, 'Oh, I see what's going on with this guy,' but also to want him, Mazin said. Of why this song in particular was selected, Mazin explained, I'm looking for a song that describes a state of permanent, lonely heartache that can never be soothed. And I'm also looking for a song that isn't overplayed, that didn't feel cliché, or syrupy, or gloppy.Mazin wound up texting his friend Sirius/XM host Seth Rudetsky for a suggestion. He said Rudetsky delivered the Ronstadt suggestion in about four seconds.