When Sark was brought in to APO, he had to wear a bag over his head, presumably to prevent him from discovering its location. Apparently no such precaution was required when bringing Irina to the top secret location, however.
Number 47: When Marshall examines the data from Lucien's PDA, there are two reference numbers with 47 one starts with 47 and one, as seen, is ref# 547-43-****
When Irina says "Jack, I understand why you believed you had to kill me, but the truth is, if the situation had been reversed, I would've found another way." It is a lot like when Sydney tells Vaughn if it had been him who had been killed or missing, she wouldn't have given up, she would have found another way.
In the embassy scene, Irina was wearing a wedding ring.
(Jack confronts the Project Helix Irina clone with out knowing it)
Jack: Tell me Irina, how did it feel giving the order? Was it difficult ? Were you able to remain cold, indifferent? Were you amused?
Irina Clone: Jack this is cryptic even for you.
Jack: Then let me be clear… how did it feel to pay a man… to kill your own daughter.
Irina Clone: You weren't supposed to find out.
Jack: You didn't feel a thing did you?
Marshall: (about the giant Mueller Device over Sovogda) So what you're saying is a large red ball, plus contaminated water equals a city full of homicidal maniacs? There's a sentence I never thought I'd say.
Sydney: I know who you've betrayed… if you don't tell me what you know…
Nassard: You haven't been watching the news lately have you? You're too late sweetheart, it's the end of the world, or haven't you heard? Black mail is not as effective as it was once.
Irina: (about Jack shooting her Project Helix clone) Jack, I understand why you believed you had to kill me, but the truth is if the situation had been reversed… I would have a found another way.
Irina: About my indiscretion with Sloane- I can hope you'll accept my apology.
Jack: Of all the things you've done, that's what you're going to apologize for? (they smile at each other)
Vaughn: We've been tasked to rescue a woman who killed my father- your mother, who is supposes to be dead, by the way, and to disable a giant red ball floating over a Russian city.
Sydney: Crazier things have happened.
Vaughn: But what's the point? I mean, the weirdest terrorist attack of all time?
Jack: Their purpose remains a mystery. Perhaps Sovogda serves some strategic importance.
Weiss: I'd go with world domination, but that's always my go-to.
Vaughn: How do you want to play this?
Sydney: You mean you want to be rough or you want me to be rough?
Vaughn: Oh, you're always rough.
Sydney: No, I'm not!
Vaughn: Yes you are.
Sydney: That's not true.
Vaughn: Yes it is.
Sydney: Are you talking about at home or on ops?
Vaughn: Both. Hey, I'm not complaining.
Sydney: If I'm rough, it's because you like it when I... Are we on coms!?
Jack: YES, you are both on coms right now!
Jack: You are going to enjoy getting to know Nadia. She is exceptional.
Irina: I wonder where she got that from?
Music from this episode includes:
"My Neck, My Back" by Khia
Carl Lumbly does not appear in this episode - presumably as Dixon is recovering in hospital after being shot by Elena in the previous episode.
This is the only episode of the whole series without Ron Rifkin (Sloane).