This was a weird situation where two completely random dialog lists lined up to tell a story...
So when Blackwood came out I created a new character (Stamcro) and started travelling around with Mirri, who I have specced out as a healer. I've mostly tuned out her random dialog, though for the most part I like that she's cheerfully irreverent. After Blackwood I started going through the standard Alliance storyline, and my character finally hit Bangkorai so I was taking him through the final Mages guild quest to claim Eyevea, which of course is where Valaste goes crazy. So at one point I'm roaming around Eyevea killing Daedra, with both Mirri and Valaste in tow.
This is, of course, just before Valaste loses it, so she's spouting random comments about being tired, and getting tired of fighting, and wondering if the Daedra will ever end, etc. And Mirri is saying her usual lines. I'm not really paying attention to either, but I do notice that they appear to be taking turns -- first Valaste says something, then Mirri, then Valaste, then Mirri, and so on. I'm halfway through the outer perimeter circuit (when you're collecting magic focus crystals) when Valaste complains about how there doesn't seem to be any end of the Daedra. It's one of the random speech choices she's already said a few times, so I roll my eyes a little.
Then I hear a sigh.
The sigh is probably Valaste -- I don't remember a sigh being part of Mirri's speech list, and it seems to fit with the other kinds of things Valaste says, and reflects her mental state pretty well, but at this point I'm used to the Valaste/Mirri/Valaste/Mirri pattern so I automatically associate it with Mirri. And at that point, the entire context of the conversation rewrites itself in my head -- Suddenly it's obvious that Valaste is really pissing Mirri off, and she's been trying to act cheerful and ignore Valaste as best she can, but she has, in that moment, reached the end of her rope.
Obviously Mirri isn't saying anything new, and obviously the way she says it doesn't change, because it's all pre-recorded audio files, but it really does start to feel different. The next time Mirri says "I'm still here... thanks for asking" she's not saying it to my character, she's saying it to Valaste. When she says "do you think it would kill them to run away? Obviously not... maybe they should try that" she's telling me to ditch the crazy elf. But the thing that really slew me was when she said "maybe I should have become a Buoyant Armiger" because I imagined her saying that with a rigid smile, showing all her teeth, as she questioned all her life choices up to that point.
It was amazing. It was all purely random, and if I hadn't heard (or imagined, I guess?) that sigh when I did I never would have started making that association... but it worked so well!