It's the one where Kira gets trapped in a stone formation that grows to swallow her up while she's in some caves with Odo, and he confesses her love to her, and she says she loves him too, and that's how he knows that it's not Kira but rather a changeling. ;_;
ODO: I wish there was something else I could do...
KIRA: Just keep talking to me.
ODO: What do you want me to say?
KIRA: Anything. Tell me a story.
ODO: A story?
KIRA: I know. Tell me how you got your name.
ODO: My name? Come to think of it, that is an amusing story.
KIRA: Tell it to me.
ODO: Well, as you know, when Doctor Mora first brought me to his laboratory, it was under Cardassian supervision. All specimens had to be clearly labeled in Cardassian, so that the overseers would always know what the scientists were working on. Since no one could decide exactly what I was, Mora labelled me "Unknown Sample," which the overseer translated into Cardassian as "Odo'ital."
KIRA: So your name is "Unknown Sample?"
ODO: No. "Odo'ital" literally means "Nothing." Even after it became clear that I was sentient, the Bajoran scientists kept calling me that. As a joke, they split it into two words, like a Bajoran name: "Odo Ital." Which eventually got shortened...
KIRA: To Odo.
ODO (nodding): But the thing is, for the longest time, when anyone spoke my name, the first thing I'd think of was what it meant: "Nothing." What better way to describe me? I had no family, no friends, no place where I belonged. I thought it was the most appropriate name anyone could give me. (a beat) And then I met you... (pause, then he starts covering) And the others. Sisko, Dax, even Quark. And now, when I hear one of you call me "Odo," I no longer think of myself as "Nothing." I think of myself as... me.
OMG identity issues and love. ;_; They're even a little like Rinali's. Except more obsessively focused on one person (although the others do matter to Odo, just, uh, not a fraction as much as Kira does). And the way he breaks down when he tells "her" that he loves her--she practically has to tear it out of him. The script reads (and Rene Auberjonois does a fine job of conveying):
"[He] just said the hardest thing he's ever had to say. Odo slumps down against a wall of the cavern, ashamed, exhausted, and heartbroken. He can't even look at her."
I love him. ;_; And this episode makes me love Odo/Kira (what with the female changeling all "she'll never love you back, you're a changeling"), when before I was just like "meh, it's okay if it stays one-sided." Why did they have to screw it up? DAMN YOU VIC FONTAINE.
However, I do feel rather cheated that Garak isn't in this episode I'm watching now about Cardassian scientists showing up on DS9. It's an episode about how Cardassians start to show up on the station! How could they leave him out? Woe. I suppose I will have to content myself that I'm only a few episodes away from "Distant Voices" in my backlog, and that's an episode where Bashir goes through a Metaphorical Experience in his mind and meets various different people who symbolize different aspects of his self, and I know Garak is in that one, and aljfdkslhglgdkgwei OTP.