Three sets of young hooves trotted down Mane Street, their owners companionably clustered close and chatting cheerfully in the face of the persistent mists of drizzle that beaded on their coats and in their manes. The blazing oranges and yellows of autumn had faded since the Running of the Leaves, and now only scattered remnants of the leaves remained, their colours faded to darkening brown where they lay plastered across Ponyville's worn cobbles by the rain.

The Unicorn of the mismatched trio rolled her eyes as the others teased her about the scarf that her sister had insisted she wear despite the mild temperature. Not just insisted, but gushed on and on about style and panache and a bunch of other hooey. To her it was just a scarf, but she knew better than to express that opinion when her sister was in full flow. Besides, Rarity meant well and she knew just how much it would please her to wear it. And it is kinda nice, I guess.

The weather for the preceding week had been thoroughly miserable, and had barely lifted enough in the early afternoon for them to get together outside of school – and, for a change, they had done just that. No school, no crusading, no scooters, just best friends spending time with each other over a milkshake at the café.

She was jolted out of her thoughts when she realised that Scootaloo had stopped abruptly, cocking her head to one side.

“You guys hear that?”

She opened her mouth to ask, 'Hear what', but then she caught it herself. A single, high-pitched note growing in strength, coming from the south. Her friends seemed to reach the same conclusion and together, they turned to look in that direction. She could feel a slight rumble beneath her hooves and nervously backed up onto the pavement. The noise was really getting loud now, and suddenly a pale-green form rounded Quills and Sofas and shot past them at a flat-out gallop, ears flat, eyes rolling in terror, the monotone scream suddenly changing pitch as the pony whipped past them like its tail was on fire.

“eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeEEEEEEEEEEEEEEEEEEEEEEEEeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee!”

Gobsmacked, they watched it go. Scootaloo was the first to recover her voice. “Uh... was that Lyra?”

Apple Bloom swallowed loudly. “Yup.”

“Is there something chasing her?”

“Nope.”

Sweetie Belle dragged her eyes away from the fleeing figure to look back the way she had come. “You sure about that, 'Bloom? I mean, ponies don't usually stampede like that, 'less the hounds of Tartarus are on their tails.”

“Or they jus' spit their bit,” said Apple Bloom philosophically. “Wouldn't be the first time.” With a shrug, she turned to continue on their way. “Y'all coming?”

Sweetie Belle and Scootaloo looked at each other and fell back in beside their friend.

“You don't think that was just a little bit odd?” Sweetie Belle persisted.

Apple Bloom looked over at her with a grin. “In Ponyville? Not really!”

At the foot of the bridge over the Ponyville brook, they went their separate ways, but the strange sight stuck in her mind during the short walk back to the Carousel Boutique. With a brisk shake at the door, she nosed her way inside.

At the sound of the chimes hung above the door her sister's voice rang out in its practised manner. “Welcome to Carousel Boutique, where every ga-” Rarity pranced into view and her spiel wound down abruptly as she surveyed the bedraggled filly dripping on the mat. “Oh, Sweetie, darling!”

She tried to endure the fuss with good grace as her sister swathed her in towels, clucking and tutting like an old mother hen.

“...no, no, hang it lengthways, lengthways, it's alpaca and merino! Do you know long it took me to persuade Al Pacachino and Baabara to part with that wool? I suppose it's salvageable, just so long as it doesn't stretch. Ugh, wipe that mud off your fetlocks with the second demi-hoof towel. No, no, no, the cotton weave, not the terrycloth! Honestly, Sweetie...”

She let the words wash over her, blindly following directions until she was deemed suitable to pass through the showroom, Rarity's sanctum sanctorum, and into the kitchen.

Rarity was still chuntering away in a distracted manner as she filled the kettle and made hot chocolate, which was plonked on the kitchen table in a manner that said, drink this – or else! Given that she was starting to feel a bit of a chill from her damp coat and that Rarity made excellent hot chocolate, she was more than happy to obey.

To her surprise, her sister joined her. Blowing out a long sigh of satisfaction, she asked, “So, what catastrophic mayhem did you and your friends wreak to today?”

She opened her mouth to protest at the assumption of disaster, then saw the grin hovering on her sister's face. Making a face, she started to talk about her day.

“It sounds like you three had a grand time,” said Rarity when she'd finished, with an indulgent smile. “I'm glad you had such a nice day, even if the weather wasn't the best.”

Talking about it had kept the peculiar fleeing, screaming pony in her mind, though. Maybe Rarity would know?

“There was one strange thing when we were on our way back here. We could hear somepony screaming, and then Lyra ran up Mane Street howling at the top of her lungs. It was really weird.”

Rarity looked away and mumbled something that sounded like, “Shedding anxiety.”

Sweetie Belle blinked in incomprehension. “What the what-now? Shedding?”

Rarity turned back to her with an uncomfortable smile on her face. “It's nothing that you need to worry about just yet, Sweetie.”

Her ears pricked forward the typical adult evasion. “You mean I will have to worry about it someday? What is it?”

“Well...”

“Aw, come on, Rarity!”

Rarity sighed again and raised her eyes to the ceiling. “Why do I always have to be the one to do this? Why can't Mum and Dad take care of it for once?” Refocussing on her sister, she took a deep breath. “Have they taught you anything about ponies' bodies and growing up at school?”

Yuck. “You mean the birds and the bees and all that stuff?” she said reluctantly. “Sure. I never did figure out what that has to do with ponies having foals, but yeah.”

Rarity shuddered. “Y-you'll work it out when you're older. Much older. Now, when you reach a certain age, Sweetie, your body starts to change. It's all perfectly normal and a part of growing up, but for Unicorns there's something else that nopony else has to go through.”

Sweetie leaned forward, both puzzled and intrigued. “Something that only affects Unicorns? Something to do with your magic and stuff?”

“Well... yes. In a manner of speaking. It's to do with your horn. Do you know what horns are made of?”

“The same stuff as our hooves?”

“That's right! The thing is, though... you see the thing is...”

“What? What? I mean, you're making it sound like they drop off, or something.”

Rarity heaved a sigh of relief. “Oh good, so you already knew.”

Sweetie Belle's screech of disbelief effortlessly reached the upper registers. “It does?!”

“Ah. That'd be 'No', then. Oh dear. Look, it's perfectly natural! After a while, the horn gets worn and abraded, and if a pony uses lots of magic it starts to thicken and build up a resistant layer. So once a pony reaches a certain age, they start to shed their horn regularly to let a new one grow in its place. It's quite common among horned animals – like deer, for example.”

“Common in deer! I'm a pony, I'm not a deer!”

Rarity gave her a cautious grin, “You really are a dear, sometimes, you know?”

“That's not funny!”

“Sorry, Sweetie. Anyway, every three years, adult Unicorns shed their horn in late autumn, and a new one grows in its place over the course of the winter. It's quite a stressful time, as you can imagine, and occasionally some ponies get a little overwhelmed. They call it Shedding Anxiety. Lyra always was the excitable sort.”

Sweetie Belle's mind was racing, still aghast at the thought that something that basically defined a Unicorn could be lost. “So it just... drops off? Can you still do magic? I mean, I can't really do much yet, but do you have to live like an Earth pony for a whole winter, or what?”

Rairty tittered, “Oh, yes, of course you can still do magic. All the magical pathways are still there in the horn bud. In fact, sometimes it's a little easier if there's been a thick, resistant layer on the old one. Also, if a Unicorn has been unlucky enough to damage or break their horn, it'll grow back at this point.”

A horrible thought struck her. “Does this happen to the Princesses, too? I've never heard of Princess Celestia not having a horn.”

“Oh, no, no, no, the Alicorn doesn't shed. Apparently, their biology is a little different. A good thing, too – I can't imagine what havoc a shedding Twilight would get up to!” she added in an undertone.

“That's terrible! It's a blight on Unicorns! It's so unfair!” Sweetie Belle whined, clutching her horn in her hooves.

“Now Sweetie, each of the Three Tribes has their own little burdens to shoulder. Ha! Trust me – you haven't seen Rainbow Dash in moulting season. Why, Fluttershy won't even leave the house when she's in moult. A nasty episode which left her with one nearly-naked wing, she tells me.”

Sweetie Belle shook her head slowly. “How come I haven't noticed this before? I mean, there's you, and Mum and Dad, and loads of Unicorns around?”

“Most Unicorns find it rather embarrassing, so it's sort of a secret.”

Reluctantly, Rarity reached up and wiggled her horn between her hooves. There was a noise like a dry cork leaving a bottle, and suddenly her she was holding a hollow husk of keratin. A little nubbin of flesh stood out where the horn had been, pulsing very faintly blue with Rarity's magic aura.

Sweetie Belle couldn't stop staring at her sister as an almost-Earth pony, and Rarity quickly began to fidget, shaking her mane down over her forehead.

“Yes, yes. Now that you know about it, you'll probably start to see when ponies are trying to hide that they've shed. Fake horns, odd haircuts, that sort of thing. Of course, it's always fantastic news for me – even with the inconvenience.”

“What? Why?”

Rarity fixed her with a look over the top of the reading glasses perched on the end of her muzzle.

“Are you kidding me? I make an absolute fortune on hats.”

Author's Notes:

No, I can't explain this one, either.
Brought on by a discussion about the nature of Unicorn horns.