Mad Science whispers to Chuck about how he can forget about Sarah, Ellie, Morgan and Awesome: They will all stop loving him without the Intersect, and he will be nothing, and he will lose them all. You'd think that would do it, right? Not a terribly evil plan. Poor villainous mad scientist. I guess when your supervillain technology consists entirely of saying Mean Girl shit, you get used to getting whatever you want. On the other hand, disappointing Captain Awesome would kill me because not only is he great -- sucks for me -- but he would be sad -- sucks for the world.
Sarah's girling out back home, crying on the bed without fucking up her makeup and rolling around on the bed and Brokebacking Chuck's clothes and smelling his smell and suddenly she's found a folded-up weird map in his Nerd Herd pocket protector, while this very Josh Schwartz song plays that will play again at the end. Morgan shows up to check on her, and says he's had an awful taste in his mouth that -- "strange twin thing" -- makes him think Chuck's been eating "something icky," and even though that's great, Sarah doesn't have time to worry about it.
Five seconds later for no real reason, Morgan freaks out -- "I fold!" -- and admits that the weird map is one iteration of Chuck's proposal plan. I don't remember if we knew about this because on TV, straight people are constantly pulling out rings and gazing at them like Gollum and thinking about proposing to each other. Maybe in real life also they do this. Sometimes they end up going through with it, sometimes they don't, but I rarely commit it to memory.
Anyway, it's a combination of things that are important to both of them, but mostly things that were important to Chuck when he was (more of) a dorky teenager (than he is now): DeLoreans, a Wyld Stallyn, a Lamborghini. Sarah is blamflasted because she totally wants to marry Chuck the day he grows into asking her, and Morgan -- this whole episode is really subtle -- goes, "Ever since he lost the Intersect, the proposal plan got put on hold. Chuck knows that you love him, Sarah, okay, it's just you're kind of a big fish, you know, and to a regular guy with no supercomputer in his brain, I've got to think that that's pretty intimidating."