Walter's humming a tune as he affixes his brain-tampering headgear to Olivia (who is still William Bell). Apparently they're playing "Name That Tune" but it seems to be the worst game of Name That Tune ever because Walter can't hum and Bell doesn't even know the right names of well-known songs like "The Girl From Ipanema" which isn't even the song Walter's humming anyway. It seems this has been going on a while, because Bell wants Walter to "try something else" and Walter says Bell is taking all the fun out of it, which hardly seems possible, as it looks like everyone is having a shitload of fun.
Walter checks with Peter to make sure the temperature is correct (64 degrees) and then with "Astro" to see if she's ready. Astrid has apparently decided to fight absentminded-professor fire with fire, and shoots back with, "Just about, Wally," which actually startles him.
Peter wants to make sure this is safe, and Walter says, "Perfectly. If everything goes according to plan, the electrical current will latch onto the dominant consciousness which is Belly's and coax it into its new residence." That's great, because things always go according to plan here, right? Saying "If everything goes according to plan" on Fringe means exactly what "Barring some unforeseen circumstances" did on Seinfeld: it meant shit is about to go down.
The "new residence" that Walter is talking about is the corpse -- being kept cool by hundreds of ice cubes -- laid out on a slab near Peter, who is still all grouchy with his arms crossed because he wants to know if this will be safe for Olivia. "No offence," he says to Bell, who takes none. Walter says Olivia's mind is still peacefully at rest and won't be aware of any of this. But he still wants everyone to take a few steps back. This doesn't exactly fill Peter with confidence, but maybe he just means that Bell's been eating a lot of cheese today.
Anyway, Walter asks Belly if he's ready, and Belly responds with a chipper "Aye aye, captain," because these two guys are still having the time of their lives, and Astrid flips the switch or pushes the button or whatever and then the corpse wriggles and writhes and ripples, partly because of the electrical current but also because this guy clearly wasn't a prime physical specimen even when he was alive. Then there is crackling and popping and the lights go out, but the corpse has not been reanimated, and Bell is still inside Olivia, still not in the way Peter wants to be.