"What do you mean, TEN fingers?" Twilight asked over her sandwich plate.
"You know," Rarity said. "Two hands, five fingers on each hand." She pursed her lips momentarily. "Or are you counting the feet, too? I suppose you could...no. The human world's Rarity was very clear on this, when I wrote her asking about human couture. The foot fingers are called toes, and they don't count as fingers."
Fluttershy remarked, "There are a few cats who have extra fingers and toes. I met a whole passel of them, when I visited the Historic Hemmingandhawingway House in Flora Da last year." She gazed at Twilight. "Is THAT what you meant?"
"No," Twilight insisted. She shook her head. "I suppose you just had to be there."
***
Immediately after the luncheon, Rarity went home and wrote a letter to her human world counterpart. She wrote the address very carefully and neatly on the envelope, affixed a stamp, sealed the letter inside, and went outside to wait by her mailbox.
A few minutes later, Ditzy Doo Hooves happened by on her usual delivery route. "Hello, Rarity!" Ditzy said cheerfully, blinking her eyes slightly out of sych with each other.
Seeing this, Rarity felt dizzy. The elegant unicorn sank down onto her haunches. "Ditzy, darling? Do you still make that SPECIAL extra little swing on your route?"
"Do I! Lately I've been handling more of THAT mail than ever!" Ditzy smiled. "It's a really fun flight! Well, whenever I show the extra loop to any of my coworkers and they try to follow me, they always end up getting nauseous and crashing. But I like it a lot! It's like flying fifteen or twenty swoops and loops all at the same time!"
Rarity nodded calmly, and held out the envelope. "Could you be so kind as to deliver this one for me?" she asked.
"Sure!" Ditzy saluted, and accepted the envelope. "See you later, Rarity!"
Rarity watched as Ditzy flapped her wings, rose into the air, flew a wild, swooping barrel roll, and vanished about halfway through.
"Huh," Rarity said.
***
Two days later, Rarity found a reply in her mailbox. She carefully opened the envelope, pulled out the letter, smoothed it flat with her magic, and read it.
She read it a second time, just to make sure.
"Huh," she said. "I suppose this DOES explain a few things."
***
As five friends lunched together al fresco outside a Ponyville cafe (Pinkie was missing for some reason) Rarity's delicate unicorn magic pulled an envelope from her saddlebag. She looked across the table at Twilight, and said, "Dear? I think...there's something we might want to talk about."
"Sure!" Twilight said with a smile. "So talk."
"When you went through the Mirror Portal, your body changed, right?"
Twilight smiled. "Of course it did! My legs got all long and weird. My face got kind of flat. And my hooves turned into those weird bunches of tentacles. We talked about that just last week."
"Yes," Rarity said. "On another note...do you know that some ponies can be mares in their minds and hearts, and stallions in their bodies? Or the other way around?"
Twilight's eyes went big. "Oh!" She reached out one hoof across the table, to touch one of Rarity's. "You're trying to figure out how to break the news to me about Big Mac." Twilight reassuringly patted Rarity's hoof. "Don't worry, Rarity, I know all about it, and I think it's fine. I'm so glad that Apple Bloom has a brother AND two sisters, who all love her and want her to be happy."
Twilight sighed contentedly. "I think it's wonderful."
Rarity said, "All those sudden changes and differences in your body, when you went through the Portal. Did you find that hard to adjust to?"
Twilight shrugged. "For a few minutes, sure. Well, maybe longer if you count that I didn't have my unicorn magic, and it's harder to write with your mouth if you aren't used to it--"
Rarity interrupted. "While you were in the human world, did you ever have to visit the...facilities?"
Twilight guffawed. "It wasn't hard at all. They have sitdown toilets just like we have here. That was probably the easiest thing."
"And did you have any trouble FINDING those facilities?"
Twilight shook her head. "The doors are even the same. M for mares...I don't know what they use for stallions. But M for mares is the same. See, easy?"
Applejack started laughing. When the other ponies stared at her, she said, "Sorry, Ah didn't mean to interrupt. Ah'm really enjoyin' your story, Twilight."
"What story?" Twilight asked. "I just told you one fact."
Rarity nodded. "Twilight? While you were in the human world, where did you sleep?"
Twilight looked a little sad. "At first, I slept in the school library." She took a deep breath, and sighed. "That was so wonderful. Me and a whole new world of books, sleeping together all night long."
Her face changed, to look just a little peeved. "But when the human girls and the teachers found out, they said it was weird and I had to stop." She shook her head. "Maybe I never should have told them."
Twilight's head tilted noncommitally, and she smiled again. "But when they wanted me to STOP sleeping in the library, they invited me for sleepovers, and that's fun too!"
Rarity asked, "On account of the DIFFERENCES between you and...the girls there at the slumber party, was there any awkwardness? Any unexpected surprises?"
Twilight laughed nasally. "I'll say! We ponies can go around naked all the time except for special occasions. But did you know in the human world, they think that's weird?"
Rarity replied with a fixed expression. "Yes. I knew. I've been writing letters back and forth with the human Rarity for weeks now. And something else I think you should know..." Rarity's voice trailed off.
After about half a minute of awkward silence, Fluttershy asked, "So are the humans in that world kind of like cats in ours? On account of the toes and fingers..." She blushed, and whispered, "Sorry. I didn't mean to interrupt."
Rarity stood up, leaning over the table towards Twilight. "Tell us about your eleventh finger, Twilight! Tell us HOW YOU NEVER EVEN GUESSED THAT SOMETHING WAS DIFFERENT! WHEN THE GIRLS DIDN'T WANT YOU AND THEM TO EVER BE NAKED IN FRONT OF EACH OTHER!"
Twilight blinked. "Rarity. I never expected an outburst like this, from you."
Rarity jumped up and down. "How could you NEVER have FIGURED OUT?"
Twilight blinked again. "Well, of COURSE the human world is different--"
Rarity screamed, "When you're in the human world, you turn into a STALLION!" Her voice became less loud. "Or whatever the human equivalent is." She blushed a delicate pink.
Fluttershy said softly, "I think what Rarity is trying to tell you, Twilight, is that you're transgender. But only part of the time."
"What?" Twilight laughed. "Do you mean like a werewolf or something? But instead of a wolf...a werestallion? If that even makes sense."
Fluttershy pushed her chair back away from the table, stood, and walked around to Twilight. The gentle mare whispered in Twilight's ear for a few minutes.
Finally, Twilight said, "Oh." She looked at Rarity. "So THAT's what you meant, Rarity." Twilight blinked. "And that's why my eleventh finger has such poor fine muscle control. Do you know, I can hardly wrap it around things at all?" She shook her head. "Is EVERY stallion's organ so useless? I feel sorry for them." She shrugged. "I just thought maybe because I'm usually a pony, the transformation hadn't gone quite right and mine was defective."
Applejack pressed both her forehooves against her mouth. Her breath forced its way out in gusts of half-stifled laughter, whistling between her hooves.
Twilight sighed. "It seems like a real waste. An eleventh finger almost a third as long as my leg, and it doesn't do hardly ANYTHING of any use."
The ponies at the next table tried hard, and unsuccessfully, not to appear absolutely fascinated by this latest remark.
Twilight shrugged. "But it explains why humans wear those weird undergarments to keep them up out of the way." She looked at Rarity. "That must be why you were so interested in this. On account of the fashion opportunties."
"Yes," Rarity said flatly. "I'm sure that was it."
Pinkie walked towards the table, carrying a large box. "Sorry I had to miss some of that," she explained. "I had to make an emergency rush delivery for Sugarcube Corner." She blinked her big, innocent-looking blue eyes. "Did I miss anything really good?"
The other mares looked at her, wondering how to explain the last twenty minutes.
Pinkie held out a box to Twilight. "You're good at spelling. Would you check this for me? You'll have to open the top of the box."
Twilight accepted the box, put it down on the table, lifted the lid, and peered inside. Twilight recited, "Congratulations on your friends coming out to you that whenever you're in another dimension, you're a mare (we think?) in a stallion body."
Twilight took a deep breath. She slowly exhaled. She took another deep breath, and slowly released it. Finally she said, "Yes. I think this is pretty much right. Except you left out the weird ape creatures part."
Pinkie said, "I wasn't sure what the polite language was for that part, so I just kind of skipped it. You don't mind, do you?" Pinkie put a party hat on her own head. She put a second hat on Twilight.
Twilight lifted the cake out of the box. "I don't mind at all, Pinkie." She smiled. "In fact, I think this is the best coming out party that I've ever had in my life."
Pinkie whispered, "So far."