Near the end of the episode, Gowron tells Worf that he (Worf) will not get another chance to kill Gowron. However, Worf does kill Gowron during the Season 7 episode, "Tacking Into the Wind."
It is established in this episode that Worf is second in command of the Defiant, behind Captain Sisko.
Goof: Time Index 39:12. After Martok stabs the two guards, there is no blood on his knives.
Nitpick: Even though they are going undercover, Worf's appearance is unaltered, despite the fact that a Klingon could recognize him (Gowron and Martok specifically).
Nitpick: The shot of the damaged Rio Grande returning to the station is recycled from part of the damaged Volga returning two episodes ago.
O'Brien: It's not easy being funny wearing these teeth.
Quark: Captain, you're just in time for happy hour.
Sisko: Do I look happy, Quark?
Dukat: (amused by Sisko's Klingon disguise) Captain, I insist we make a holographic record of the four of you. Consider it payment in full for the use of my vessel.
O'Brien: Maybe after the mission.
Damar: After the mission you'll all be dead.
Sisko: How long have you suspected?
Martok: Months. I've known Gowron a long time. And it is no secret that we have not always agreed on the way he runs the Empire. He is a politician! Too eager to compromise! Too eager to talk! Last year he stopped the attack on Deep Space Nine instead of going to war with the Federation - and then he changed. Suddenly he was the one calling for war.
O'Brien: I would have thought that would make you happy.
Martok: At first it did. But after the war began, he started ignoring the counsel of his Generals, throwing aside all wisdom in his pursuit of victory - our losses continued to mount and still he listens to no one!
Odo: No one but the Founders.
O'Brien: So, let me get this straight: all we have to do is get past an enemy fleet, avoid a tachyon detection grid, beam into the middle of Klingon headquarters and avoid the Brotherhood of the Sword long enough to set these things up and activate them in front of Gowron?
Worf: If we succeed, there will be many songs sung in our honor.
O'Brien: Let's hope we're there to hear them.
Dukat: I hope First Minister Shakaar appreciates what a lucky man he is.
Kira: Shakaar's not the father.
Dukat: Then who is?
Kira: Chief O'Brien.
The reason Lieutenant Dax does not join the mission, despite her immense familiarity with the Klingons, is because Terry Farrell's skin was allergic to the makeup.
Marc Alaimo, best known for his role as Dukat, has played numerous characters in the Trek universe. He played Gul Macet on TNG episode "The Wounded," Frederick LaRouque on the episode "Time's Arrow (Part 1)", Antican Delegate on the episode "Lonely Among Us", and Tebok on the episode "The Neutral Zone".
J.G Hertzler, in addition to his recurring role as Martok, has played numerous roles in the Star Trek universe. On DS9 he played the role of Roy on the episode "Far Beyond The Stars", Vulcan Captain on the episode "Emissary Part 1 and 2", and Laas on the episode "Chimera". On Enterprise he played Klingon Captain on the episode "Borderland (Part 1)" and Kolos on the episode "Judgment". On Voyager he played Hirogen Hunter in the episode "Tsunkatse".
Dax shows the senior staff a graphic labeled Polaron Emitter Prototype X-47. 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.
Martok believes he and O'Brien fought together at Mempa. During the Klingon Civil War, the Mempa Sector was the site of a battle between Gowron's forces and those of Duras, in the Next Generation's "Redemption Part 2".
The original script for this episode had Gowron as the changeling, but it was changed to General Martok after the writers decided that they needed to surprise the audience.
In one scene Kira blames Bashir for getting her pregnant. This is an inside joke as Nana Visitor and Alexander Siddig were expecting their first child at the time.
Among the statues in the Hall of Warriors, General Chang from The Undiscovered Country is there.
In the post title sequence scene, this is the first time since the Season 4 episode "Body Parts" that you can see the Ferengi Commerce Authority's stickers on Quark's door prohibiting any Ferengis from doing business there.