"My mind was filled with images... Thoughts of me, yet I was not entirely myself."
— Teal'c
Teal'c begins to suffer from strange dreams in which he lives an ordinary life as a human firefighter named "T" — or alternatively, a human firefighter has dreams of being an alien called "Teal'c". As he continues to experience two seemingly parallel lives, it becomes increasingly difficult for Teal'c to determine which scenario is the reality and which is fiction.
"The Changeling" provides examples of the following tropes:
- But You Were There, and You, and You: In the "firefighter" sequences, the other members of the cast take on various roles in "T"'s life; O'Neill is the Fire Chief, Carter is The Captain, Jonas is a probationary firefighter referred to as "Probie", Bra'tac is his stepfather "Brae", and Shan'auc reappears as his wife "Shauna", while Apophis makes various appearances as a hallucination or in a dream. Daniel also shows up as the hospital psychologist, but unlike everybody else it turns out that he's actually real.
- Catapult Nightmare: Happens at the beginning of the episode, with "T" waking up from a nightmare where he's about to be operated on by Apophis.
- Chekhov's Gun: Jacob reveals that the Tok'ra have developed a modified version of the tretonin used on Pangar that can be used to provide Teal'c and Bra'tac with an immune system in lieu of a symbiote.
- Continuity Nod:
- Shan'auc appears in the "firefighter" reality as Teal'c's wife, Shauna.
- Fraiser mentions that a Jaffa deprived of their symbiote for an extended period of time will often have their life flash before their eyes.
- Crucified Hero Shot: Teal'c gets one when the camera pans out to show him and Bra'tac as the sole survivors among dozens of slaughtered Jaffa.
- Cuckoo Nest: Doesn't involve an asylum, but the basic premise is the same, with Teal'c switching back and forth between his "normal" life at the SGC and a reality in which he's a human firefighter and becoming increasingly confused about which one is real. As it turns out, they're both fictional, and in reality Teal'c is slowly dying on another planet as he shares his symbiote with Bra'tac.
- Determinator: Both Fraiser and Daniel outright state that it must have taken nerves of steel for Teal'c to keep swapping the symbiote back and forth between himself and Bra'tac for three days straight.
- Dream Walker: It turns out that psychologist!Daniel is the real thing, appearing to Teal'c in his dream to try and help him face the reality of the situation.
- Expo Speak Gag:Carter: Why don't you try a glass of warm milk?Teal'c: I would prefer not to consume bovine lactose at any temperature.
- Fever Dream Episode: Most of the episode takes place inside a delirious Teal'c's head as he nears death.
- Foreshadowing: Several hints are dropped that Daniel isn't part of Teal'c's dream:
- When "T" first meets Daniel, Daniel says they might've met in another life, if "T" believes in that. Hinting that unlike everyone else, this is the real Daniel Jackson, and also hinting as to the nature of what's going on with Teal'c.
- At the start of the second meeting, Daniel asks "T" to tell him about his dreams (of the SGC). When "T" asks Daniel who told him, suspecting "Shauna", Daniel denies she did anything, and just says "Trust me, I just know."
- Daniel's appearance in the second meeting is preceeded by a gust of wind, similar to how the series 5 episode Revelations ends.
- Friendship Moment: The final scene, with Daniel appearing to Teal'c in the infirmary to reassure him that he's going to be okay after he's put on the tretonin.
- Have We Met?: This exchange when Daniel introduces himself to "T" as the hospital psychologist:T: You think I'm crazy.Daniel: No, not yet. We just met.T: We haven't met before?Daniel: No. No, I don't think so.T: I'm sure we have.Daniel: Well, maybe in another life or something like that. You know, if you believe in that sort of thing, some people do.
- Heroic Sacrifice: A non-lethal variant, with Teal'c giving up his symbiote to keep Bra'tac alive, paralleled in the firefighter dream by "T" donating his kidney to "Brae".
- Insistent Terminology: Teal'c is very insistent that he didn't faint after he flat-out collapses in the mess hall during one of the interludes at the SGC.
- Made of Iron: In the firefighter sequence, Brae calls out T on this after having been right next to a car whose gas tank suddenly exploded with him right next to it, and all he received was a head ache. Even more, Brae tells T that he should be frightened, making T really think about how he could have healed.
- Meaningful Echo:
- At the beginning of the episode, "Probie" says that "T" made him feel like one of the team. This is echoed at the end with the real Jonas telling Teal'c the same thing after he's brought back through the stargate on the verge of death.
- Daniel says the lines "you're just gonna have to trust me" and "that's a promise" during his appearances in Teal'c's firefighter dream, and later repeats both when he visits the real Teal'c in the infirmary after his ordeal.
- Not Afraid to Die: "Brae" claims that he is ready for death when his body begins to reject the kidney transplant, only for "T" to angrily counter that he is not ready for him to die.
- Nothing Is the Same Anymore: Teal'c's symbiote "Junior" dies and both him and Bra'tac start taking tretonin to keep themselves alive and replace their immune systems in lieu of larval Goa'ulds.
- One Character, Multiple Lives: Teal'c switches back and forth between his life at the SGC and a world where he's a human firefighter.
- Only Known by Their Nickname: Teal'c's full human name during the firefighter sequences is never revealed, with the other characters simply calling him "T" or "T-man". Though if you look closely, the name "Tyler" is written on his medical id band while in the hospital.
- Parental Substitute: Made more explicit than ever when Bra'tac takes the role of Teal'c's stepfather in his dream.
- The Reveal: About halfway through the episode it's revealed that not only are the firefighter scenes taking place in Teal'c's imagination, but so are the seemingly business-as-usual scenes in the SGC, and the real Teal'c is dying in the aftermath of what looks like a horrific battle with no immediate rescue at hand.
- Daniel revealing to "T" that he's the real Daniel Jackson watching over his friend while he goes through this ordeal.
- Shirtless Scene: Teal'c gets at least two in the firefighter reality.
- Smash Cut: Used a throughout the episode to indicate transitions between the two different "realities".
- To the Batpole!: The firefighters all slide down poles and race to their vehicles when they get their first call-out of the day.
- You Are Not Alone: As with his visits to O'Neill in "Abyss", this is pretty much the whole point of Daniel hanging around inside Teal'c's head, since he can't interfere directly.T: Hey, you can't leave me here like this!Daniel: I haven't left your side, Teal'c. And I'm not going to. That's a promise.
