[After everyone else has gone, Housecall stares at Rarity.]
Housecall: What do you have against Diamond Dogs?
Rarity: Excuse me?
Housecall: You heard me.
Rarity (a little ruffled): What, you mean besides the fact that they're dirty, ugly and smelly?
Houecall ("Well, duh"): Um, yeah.
Rarity: Well, if you must know. I was once kidnapped by Diamond Dogs. They hitched me to carts and made me work in their diamond mines, scratching diamonds out of the earth with my bare hooves! It was the most humiliating experience of my life!
[Dr. Housecall lifts his chin a little and studies Rarity for a moment.]
Housecall: No.
[Dr. Housecall smiles.]
Housecall: No. You weren't humiliated. You liked it. You liked it so much that it scared you.
Rarity: That's the most ridiculous thing I've ever--
Housecall (talking over her): You love being cleaner and prettier and more ladylike than anyone around you. Why else would you open a fancy dress boutique in an agricultural town? You sell many formal gowns to these Podunk apple farmers?
Rarity: Well! I do all right.
Housecall: But what you're really in it for is the way it lets you lord it over your neighbors. The way they make you feel like a pretty pretty little princess just by being their dirty old rural selves. It only makes sense that the dirtier the peons around you are, the cleaner you feel in comparison.
Rarity (turning away): Believe what you like, Doctor Housecall.
Housecall: Thank you! I usually do.
[Housecall is about to continue his mockery when he alerts to the sound of a little alarm bird chirping on the windowsill.]
Alarm Bird: CHIRPCHIRPCHIRP! CHIRPCHIRPCHIRP!
Rarity: What's the matter with Rainbow Dash?
Housecall (eyes narrow): I don't know.
[Housecall and Rarity rush over to the bed to find Rainbow Dash stirring, turning restlessly under the covers.]
Rarity (pulling away the covers with telekinesis): Rainbow Dash, dear, what's wroOAAAH!
[The normally sky-blue Rainbow Dash has turned a sickly green color. The camera lingers on this horrifying sight, ominous music playing in the background, and then we cut to commercial.]
* * *
[Library Interior, upstairs. Housecall is in front of the blackboard again. He has added "greenness" to the list of symptoms.]
Twilight: Rainbow Dash's house was a bust. No tamale cupcake crumbs anywhere.
Housecall: Doesn't matter now. It's not hot sauce ingestion. Our patient's turned green, not red.
Applejack (looking at Rainbow pityingly): She sure as shootin' has. Wha, she's greener than my Granny Smith!
Housecall: So what causes tummyaches, red Pegasus trails, and greenness?
Chase: We could still go with diet. Greenness and tummyaches certainly go together.
Pinkie Pie: But what about the red trails?
Fluttershy (tiny): It's confidence.
House (ignoring her, turning to Twilight instead): What did you find?
Twilight: Yexcuseme?
House: No cupcake crumbs, I got it. What was unusual?
Twilight: Just some food! And sporting equipment! And some -- oh no.
Rarity: What, Twilight?
Twilight: Tea! She had tea leaves! Just like the tea like I get from Zecora!
Fluttershy (cowering a bit): Z-- Zecora?
Pinkie Pie: Zecora's not scary! Just because she lives in the Everfree Forest doesn't make her bad!
Applejack: No, but… the Everfree Forest? Who knows what kind of fool stuff she mighta' been exposed to on the way there!
Housecall: I'm more worried about the contents of the tea this Zecora has been pumping our patient full of.
[Beat]
Housecall: And why is she drinking tea? Rock-star gymnast athlete ponies don't drink tea.
Applejack: I reckon she was tryin' everything she could to buck herself up for tha competition and get some color back in her trail. Rarity even made her a new uniform!
Rarity: Costume, Applejack, but yes. I made it with my most beautiful radiant gems, and --
[Rarity trails off as Housecall walks calmly past her and begins thwacking his head against the wall.]
Twilight: Doctor Housecall?
Housecall (rounding on the crowd): Could one of you maybe have mentioned that the red Pegasus trail predated the falling-over tummyaches?
Fluttershy (barely audible): I said it was confidence.
Pinkie Pie: What difference does that make?
Housecall: The difference it makes is that I am not at the No-Tell Livery Stable right now getting a special "pony massage" from somepony named Lapdancer, having already finished the case. We're not looking for an illness. We're looking for something the patient deliberately partook of to shine up her Pegasus trail. The tummyache is secondary to that. We need to figure out anything truly abnormal she ate or drank or wore.
[Housecall thinks for a moment, then looks over at Twilight Sparkle, Fluttershy, Pinkie Pie and Applejack in turn.]
Housecall: Inky. Take Blinky, Pinky and Clydesdale there into the Everfree Forest. Find out what kind of herb-witch mumbo-jumbo the patient's been sucking down in an attempt to taste the rainbow.
Pinkie Pie: Which one of us is "Pinky"?
Housecall (ignoring her): My dirty, smelly minion and I are going to hopalong to the princess here's house and look at her "pretty glowing gemstones".
[Chase smiles and waves at Rarity. Rarity scoffs and turns away.]
Housecall: And I mean that literally.
* * *
[The Carousel Boutique, exterior, day. Housecall, Chase and Rarity walk up to the front door.]
Rarity: I don't want that disgusting canine in my dress shop.
Housecall (shrugging): Chase, you heard milady. I want you to look for anomalies on the outside of this building. Burrow around in the mud and dirt if you have to. Or even if you don't have to, but just kind of want to. Only then should you make absolutely sure to join us inside.
Chase (over Rarity's protests): Roger!
[Chase dives into a nearby flowerbed and begins burrowing.]
Housecall: I thought I handled that rather well. Now let's take a look inside your little Fortress of Atti-tude.
[The Carousel Boutique, interior. Housecall whacks the door in with a solid thrust of his cane.]
Housecall: Oh my goodness, it looks like a tacky dress shop exploded in here! Oh, wait, it's just a tacky dress shop.
Rarity (stern): I'll have you know, Doctor Housecall, that I make the most beautiful --
Housecall: Yeah, yeah. Save your pony umbrage. Show me the costume.
[Rarity, miffed, crosses to a curtained alcove and throws open the curtain. Inside the alcove, one of Rarity's pony mannequins is seen to be dressed in a golden vest studded with shimmering yellow gemstones.]
Rarity: Here it is. Rainbow Dash requested the shiniest, glowingest costume I could possibly construct. I hunted high and low for those glowing yellow gems.
Housecall: Wow. They… certainly are beautiful. You want to know what else they are?
Rarity: Dr. Housecall, I--
Housecall: MAGIC. MAG… IC.
[Rarity is a bit taken aback.]
Housecall: You don't think natural gems just glow like that all on their own, do you? Gems are rocks. You know, like those things between your ears. Something that glows that brightly has to have some other kind of energy coming off of it and you know what that energy is? It's magic!
Rarity: I just thought they were extra-pretty! Just what the customer ordered!
Housecall: Yeah, not unless the customer ordered a good ensorcelling on top of it. You… you idiot! You cursed our patient!
Rarity: I… had no idea.
[Chase shows up at the door, absolutely filthy.]
Chase: Hey guys! Nothing strange in the flowerbeds!
Housecall: Wonderful. Useless, but wonderful. Chase, much as I'd like to see you do a thorough search of this place, we need to get back to the library, like, now. I've got a spell to undo.