Goof: The uniform of the dead Defiant crew member can briefly, and very faintly, be seen to still have the outline of the Enterprise (NCC-1701) delta insignia used for Deep Space 9's "Trials and Tribble-ations", which has been removed and replaced with the Defiant's insignia for this episode.
Goof: After Archer and Mayweather come to the bridge and T'Pol says "Contact security", she's shown turning twice when the shooting takes place.
Mirror Vulcan Captain: Live long and prosper.
Mirror Zefram Cochrane: (trying the hand salute, failing, killing the Vulcan) Board their ship! Take everything you can!
Mirror Captain Forrest: This isn't like you, Jonathan. You never lusted for power and glory. That's why I trusted you at my side all these years, because you have no ambition.
Mirror Captain Forrest: (viewing Phlox's contribution to increased discipline) I think you enjoy your work too much, Doctor.
Trip: You don't want to end up like me, do you? I've absorbed enough delta rays to guarantee my grandchildren glow in the dark.
Phlox: (to a Tholian prisoner) Will you kindly die?
This is the first mirror universe episode without any of the the main characters from the normal universe present.
Footage is reused from Star Trek: First Contact, specifically the moment where Zefram Cochrane makes first contact.
The opening credits were revised for both parts of this episode. The new credits reflect historical events that occur in the mirror universe.
The mirror universe was created by writer Jerome Bixby for the Star Trek: The Original Series episode "Mirror, Mirror", which first aired October 6, 1967. Five episodes of Star Trek: Deep Space Nine are set in the mirror universe: "Crossover", "Through the Looking Glass", "Shattered Mirror", "Resurrection", and "The Emperor's New Cloak".
The opening credits contain a "moonlanding scene" just after the Apollo launch footage.
But the astronaut in question is wearing a standard Starfleet EVA suit from 200 years in the future