Back at the lab, Astrid relays to Walter what Peter and Olivia have learned, but Walter doesn't feel any closer to an answer. Out of the blue, he asks when Slater had an organ transplant. It seems Dr. Paris prescribed an anti-rejection drug. "It suggests that not only has Dr. Paris vanished, he's a quack," he says derisively. Walter's expression suddenly changes, and his eyes light up: "Unless he's a genius." Well, as we've seen from Walter for the past season and a half, the two are not necessarily mutually exclusive.
Later, Walter picks up a half-brain in a jar and holds it up to Astrid, Olivia and Peter, saying it's useless and dead. "Because when you remove brain tissue from a living body, you can keep it alive for a short time in a nutrient suspension, but eventually it will die. It's a problem I've tried to solve many times without success." Of course it is. Apparently, in addition to blood and oxygen, the brain tissue needs electrical stimulation. Which is where Dr. Paris's solution comes in: "He stored the brain tissue inside of another brain." Or three other brains, as the case may be. Peter and Olivia are like, say what? Walter turns on the overhead projectors to show them old CAT scans of the patients' brain, each with a little smudge in them that Walter says is foreign tissue. Hence the anti-rejection drugs. Walter says that also explains the patients' mental issues -- the different brain bits are incompatible, like trying to play an Xbox game in a Wii. Peter gets it -- it explains the mental distress, false memories, and delusions. "But once you remove the foreign tissue, then they're fine." I'm certainly no brain surgeon, but all of this certainly sounds like... what's the term? Bullshit? Just then Astrid gets a call from Dr. West, telling her she didn't find any connection between Dr. Paris and their hospital. But she did check into some affiliates. While Astrid listens, Olivia asks Walter why someone would do this, and whose brain the pieces came from. And how many more people must be driven sane before Newton has enough to build an entire brain? Astrid discreetly calls Peter over and whispers to him, so we know it's about Walter. After their little sidebar, Peter asks Walter to confirm that he never had visitors. "According to their records, Dr. Paris visited you on six separate occasions." Hmm. Perhaps this cure for insanity might end up working on Walter after all. Peter asks to look at Walter's head, and Walter nervously agrees, trying to put a brave face on it but just making me really sad. Peter finds a very old but visible scar on Walter's scalp, which must be why Walter is played by an actor with such a magnificent head of hair. Well, that explains a lot.. But then why are Walter's symptoms so much less severe than the others? Don't worry; we're just getting started.