On the whiteboard in Elena's lair is a list of other cities that she had targeted.
On this list (written in Cyrillic) are Moscow, Omsk, Zagreb, and Paris.
The liquid volume of the syringe changes between the shot where Elena fills the syringe and removes the air from it and the shot where she walks up to Nadia holding the syringe in her hand.
Carl Lumbly does not appear in this episode - making it the only season finale without Dixon.
For her performance in this episode Jennifer Garner received a 2005 Emmy nomination for Outstanding Lead Actress in a Drama Series.
The names on the Blackwell Index have changed from when it was accessed in the last episode, the name Weiss and Marshall take from it this time was not actually on this list when Jack went into it during "The Descent".
Again, they use that mini torch and touch the metal immediately. Unless it was a special CIA cool torch someone should have been burned.
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.
When Sloane and Sydney are standing in front of the TV looking at their own image from a camera nearby, Sydney raises the remote control to switch to another channel. However the Sydney in the picture does not move her hand.
Yanking the glass shard out of Sloane's chest the way Nadia did is an extraordinarily bad idea. The proper field procedure is to apply pressure to the wound around the glass shard. Nadia, as a field-trained agent, would have known this.
Number 47: US Army Corporal Ned Boilger's Serial Number reads 112762. 1+1+2 = 4 followed by 7. makes 47.
Number 47: The Vespertin Papers are submitted to the auction as lot 47.
In this episode we learn that Arvin Sloane and his former wife Emily has a baby, but it died during childbirth.
Goof: Considering that Nadia looks more like Irina than Sydney does, (as seen in photos in the episode "Ice,") wouldn't she have been a better choice to pose as "Laura" for Jack's "hallucination"?
Nadia's APO network login is: AGENT_087SANTOS
It's been established that Kradic is very paranoid...so why does he discuss his plans in front of the waitress? Even if the waitress wasn't Sydney, she would be a liability.
As of this episode, six actresses, have played the part of Irina Derevko/Laura Bristow.
Lena Olin: Season 2 Regular. Has played Irina, for the longest period, is usually associated with the character.
Uncredited Actress: Season 1, episode 6. First person to portray Irina, in picture's kept by Sydney.
Uncredited Actress 2: Season 1, episode 19. Second appearance of Irina, this time in a KGB briefing video, discussing her relationship, with Jack.
April Webster: Season 1, episode 22. Used in the last shot of season 1, to set up Irina as a major character in season 2. They were still auditioning for the full time role of Irina, and Lena Olin had not yet been cast.
Mia Maestro: Season 4, episode 4. Lena Olin was not available to create a set of pictures used in this episode, so Mia Maestro, who play's Nadia, her onscreen daughter, stepped in, to replace her, as Irina. She is also the 1st of two, series regulars, to play Irina Derevko, in season 4, the other is Jennifer Garner.
Jennifer Garner: Season 4, episode 18. Jennifer Garner played Irina in this episode to extract intel, from her father Jack, who, while unstable, believes she is her mother Laura [Irina].
Besides Lena Olin, Jennifer Garner has had the most substantial screen time, as Irina, and she is the only actress to play Irina, as her alias, Laura Bristow. She is also the second actress to play Irina, while playing a another main character on the show, the other is Mia Maestro.
Behind the guard at the embassy, there is a sign that says "Kun for toriseret personale", supposedly meaning "Authorized personnel only" in Danish, but it is actually quite meaningless. The correct Danish would be "Kun for autoriseret personale".