Broyles told Olivia that the Boston Police Department is sending an entry & apprehension team to where Walter's tracking chip was leading them. However, when they arrive, the tactical team is wearing FBI logos on their clothing, not BPD or POLICE.
Trivia: The glyph code for this episode is PORTAL.
Trivia: The Observer can be seen behind the white car as Peter and Olivia, along with an FBI team, go down to the men's bathroom after exiting their vehicles, while looking for Walter with the aid of the tracking device.
Security Guard: Are you Dr. Bishop?
Walter: Yes. And I'm perfectly sane.
Peter: Are you really trying to tell us that he is one of the heads they stole? Fine. Let's say for a second you're right. Frozen heads don't just get up and walk into places. I mean, the dead don't rise out of their graves and perform midnight brain surgery.
Peter: Apparently Mr. Gordon thought he was the actor Sydney Greenstreet, and went around quoting Casablanca. That's funny.
Peter: He looks a lot more like Peter Lorre. That's a joke.
Peter: Maybe some Valium would help.
Walter: You know, I don't do Valium nearly enough. That's a good idea. I'll have 50 milligrams, please.
Dr. West: Well, that... that's quite a high dosage.
Walter: I have quite a high tolerance.
Olivia: So then how does Newton read them?
Peter: In theory, he shouldn't be able to. But in theory, he should still be a frozen head. So in the department of how to make impossible things possible, what would he need to do?
Olivia: You so much as twitch, and you won't have a head left to refreeze.
Walter: Peter... I have a terrible headache... and a sudden craving for chicken wings.
Blair Brown is credited but doesn't appear.
Leonard Nimoy is credited as Special Appearance by.
Music: Trinkle, Tinkle (Thelonious Sphere Monk & John Coltrane)
Injoke: The license plate on Olivia's SUV at the sanitarium reads "1C3PO1": an Easter egg reference to C-3PO, the protocol droid from the Star Wars movies, played by Anthony Daniels.
Injoke: There are references to the works of H.P. Lovecraft scattered throughout the episode:
- Dr. West is named after Herbert West, the character in Lovecraft's Herbert West--Reanimator, and who appeared in the 1985 movie Re-Animator and its two sequels, and was played by Jeffrey Combs.
- Stuart Gordon, one of Dr. Paris' patients, is named after Stuart Gordon, the producer of Re-Animator.
- Paris' other patient, Crampton, is named after Barbara Crampton, who co-starred in Re-Animator.
- The Dunwich Medical Hospital is named after the fictional town that is the setting for Lovecraft's The Dunwich Horror.
UK: December 13, 2009 on Sky1
Latin America: January 19, 2010 on WB
Sweden: February 4, 2010 on Kanal 5
Australia: February 25, 2010 on GO!
Germany: May 17, 2010 on ProSieben
Poland: November 12, 2010 on TVN
Finland: November 24, 2010 on MTV3
Czech Republic: January 21, 2011 on Nova Cinema
Slovakia: May 14, 2012 on Markiza