It is in this episode that we first see that not all people have a duplicate in the Mirror Universe. It is made clear that Jennifer and Ben Sisko never had any children in that universe.
On Sisko's first trip to the mirror universe, he played along with the mirror Dax while she was coming on to him. It is revealed in this episode that they made love.
Nitpick: The Alliance Fleet doesn't seem to be in any rush to take back Terok Nor. They only decided to increase their speed to warp 9 after they found out the rebels were building the Defiant. Even warp 9 isn't their top speed, but perhaps they felt overly confident that they would succeed in crushing the rebellion, so they were in no rush? Where have we seen that before...?!
Nitpick: Smiley may have known the systems on DS9 from his knowledge of Terok Nor, but it is highly unlikely he obtained the schematics for the Defiant there. Being both a prototype and still-classified ship, records of it would not have been kept in DS9's files.
Intendant Kira: (about Sisko's last visit) You had me completely fooled. I really thought you were my Benjamin Sisko.
Sisko: Good, that was the idea.
Mirror-Worf: Make it so!
Smiley: That Cruiser has us in weapons range. Do we make a run for it?
Sisko: We run all right, right at it!
Smiley: Ahh! Pattern suicide.
Smiley: (referring to Mirror-Bashir) You remember Captain Bashir?
Smiley: Captain Bashir, Captain O'Brien, Captain Sisko - we may not have enough troops or ships or weapons, but we have plenty of captains!
Mirror-Garak: I was merely observing that as one of the many officers under the Intendant's command, it would be an overstatement to imply that I, alone, was responsible for our defeat.
Mirror-Worf: You're the only officer who managed to escape.
Mirror-Garak: I suppose I could've surrendered to the rebels. Groveling on the floor, begging for my life... like the Intendant.
Mirror-Worf: No. You're just trying to shift the blame away from yourself.
Mirror-Garak: Am I succeeding?
Mirror-Jadzia: I heard you were back. (before Sisko can respond, she slaps him across the face) That's for making love to me under false pretenses. I was suspicious of you from the start.
Sisko: You hid it well.
Mirror-Jadzia: If you ever touch me again... (whips out a long, curved dagger) Do you get my point?
Sisko: I hope not.
Intendant: (to a guard who's wife Kira had killed) Isn't that a coincidence! I was hoping you weren't married.
Carlos Carrasco (Klingon Officer) also played D'Ghor in the DS9 episode "The House Of Quark" and Krole on the DS9 episode "Honor Among Thieves". He also played Bahrat on the Voyager episode "Fair Trade".
Dennis Madalone (Guard) also played the role of Atul in the DS9 episode "Visionary". In TNG he played Transporter Chief Hendrick on the episode "Identity Crisis" and Ramos in the episode "Heart Of Glory". In addition, he was the stunt coordinator for dozens of DS9 and Voyager episodes.
Leslie Hoffman (Rebel) also played the role of Casino Patron on the DS9 episode "Badda-Bing, Badda-Bang".
The weapon's locker from the previous episode, "47 Weapons Locker", has apparently been moved to Ops. Sisko, Kira and O'Brien get phasers out of it before attempting to transport to the mirror universe. Writer Joe Menosky began including references to the number 47 in almost every episode of Star Trek since season four of The Next Generation. It is an in-joke, referring to The 47 Society at Pomona College in California, a college which Menosky attended.
This episode marks the death of the mirror Jennifer Sisko (Felecia M. Bell) and the actress' last appearance on the series.
The Regent: Make it so!
This is a humorous reference to Captain Picard's frequent command in the same words on The Next Generation.