"Looks like the maniac doesn't want to play anymore," Windfall said as she and Twilight returned to the main cavern at the end of the day.

The two of them had searched every open tunnel in the area of the apple tree room, but as the maze hadn't shifted once, they had no opportunity to do anything much but trot in circles. There had been no further challenges of any sort, either.

Twilight gave a non-verbal grunt of agreement.

Windfall sighed and settled down on her sleeping spot. They'd found a nice big patch of fescue a bit earlier, so she wasn't hungry, but she wasn't sleepy either. The last thing she wanted to do was to sit and think. She wished she'd had her litungkano. A bit of music would be something nice to concentrate on and wouldn't distract the princess from… whatever it was she was working on.

Twilight Sparkle had worked a bit of transformation magic on a couple of pieces of rock to make a mortar and pestle and was apparently grinding a piece of her chalk into a fine powder.

"Hey, Princess."

"Mm?" Twilight didn't look up from her task.

"How complex can you make stuff?"

That made her look up. "Stuff?"

"Yeah, like those bathtubs you made. Can you do more intricate things?"

"My transmogrification is pretty good, but I can't make compound items all at once. I could do it eventually by creating the components and then assembling them. But then there's the issue of precision, which is limited by my ability to visualize. I might be able to build a crude clock, but a small watch or something similar is beyond my skills. Why, do you have an idea?"

Windfall chuckled. The alicorn certainly loved to explain things at length. "Just something to pass the time. All I need is a dried gourd about this big—" She held her forehooves apart to show the distance. "—a big, curved stick about the size of a short garden hoe, a bunch of littler sticks, and some fine wire. I can put it together myself, if you could mojo up the pieces for me."

"Should be doable," Twilight said thoughtfully as she set down the mortar and pestle. "There's enough cellulose in the food waste to simulate the wood and gourd. There might be enough metallic oxides in these rocks to make the wire if you need brass, but I can use some of my shoes if steel is okay."

"Steel would be best, actually."

Twilight got to work without asking Windfall exactly why she wanted the stuff. The faux sticks and gourd were easy, but getting the right length and diameter for the wire took her almost an hour. When all of the components were finished she asked, "Some sort of instrument?"

"Yeah, an East Zebrican thing," Windfall replied. She had set out several sharp rock scrapers she'd made by spalling off slivers from bigger stones with the edge of her shoe. "Probably sound pretty weird to your cultured ears, but I kinda got a taste for it."

"I look forward to hearing you play," Twilight replied, and turned back to her own project.

The two mares worked silently side-by-side for a while, and then Twilight stood and gathered up her things. "I'm going to try an experiment, Windfall, and I need to concentrate on it. Please don't interrupt me until I've finished."

"Sure thing, Princess." Windfall stopped working and watched her.

Twilight walked out to the middle of the cavern, directly under the center of the opening in the roof. She stretched out her wings and began fanning them slowly over the mortar of chalk dust. As she speeded up her flapping, the dust rose in a small white whirlwind and rose toward the imitation stars. The vortex spread out as it rose and became a fairly uniform cloud in the air above her.

She then folded her wings and lit her horn. Seven small pebbles, almost exactly the same size and spherical, rose from the ground and paced themselves in a circle around her. Her horn brightened, then it blazed. It shone so brightly that Windfall had to squint her eyes against the light.

There was a sharp crack as all seven of the stones suddenly shot straight upward. If there hadn't been some strange magic sealing the cavern they would have instantly disappeared into the sky. As it was, they hung as molten little blobs just short of the lip of the overhead opening.

Windfall was just about to ask what the strange procedure was supposed to prove when something even odder happened. The stones didn't come down. They hung there, their red glow dimming, in the middle of a completely immobile cloud of chalk dust. Twilight had somehow used her magic to freeze it all in place. Then the entire static structure sank downward until it was eye level with Twilight.

The princess produced a measuring stick, a pencil, and a notebook, and apparently began measuring the ripples and distortions in the cloud. She worked her way through the structure, shaving sections away as she advanced and letting them drift to the ground behind her. All the while she scribbled furiously in her notebook.

Windfall went back to building her litungkano. Twilight would explain it to her in good time, she was certain.

By the time Twilight had made all her notes and measurements, and Windfall had finished the body, neck, and tuning pegs of her instrument, they were both yawning.

"If this place isn't going to kill us— at least, not yet— then there's not much point in standing watch is there?" Twilight asked as she neatened her paperwork and carefully stowed it in her saddlebag.

Windfall shrugged. "I suppose not."

"But I still want to be cautious. That soft patch is big enough for both of us," Twilight said, indicating the pegasus's sleeping spot. "Why don't we sleep back to back, and I'll throw a little shield over us. Would that be okay?"

Windfall snorted. "More than once, I've slept in a muddy hole in the ground with a half-dozen dirty, sweaty soldiers, Princess! I ain't particular!"

Twilight walked over and lay down next to her. "You'll have to tell me about it sometime."

Windfall laughed out loud. "It stank and was uncomfortable as Tartarus. End of story."

"Well," Twilight said, as she wiggled a hip-hole in the soft dirt, "this should be a step up from that."

In the morning the two mares made a quick foray into the tunnels to confirm that the labyrinth hadn't shifted while they were sleeping, and then returned to the big cavern by way of the carrot chamber.

"No point in searching until it changes, right?" Windfall asked, munching on her breakfast as she walked.

"No, we won't be able to map the rest, or get to the apple tree room until it does," Twilight agreed. "It's fine with me, though. I have enough calculating to do to fill the rest of the day."

"Oh yeah, all that measuring you did last night. What's up with that anyway?"

"I want to graph the thaumic waveforms of the n-dimensional hypervolume that makes up the barrier…"

Twilight paused and looked back at Windfall, who had stopped dead in the tunnel with a big wad carrot in one cheek.

"You wanna put that in Equuish, Princess?" she said, spraying a little bit of half-chewed carrot.

Twilight had the good grace to blush just a little. "I'm trying to work out what type of magic is holding us here and exactly how strong it is."

Windfall nodded, and resumed walking. "Shoulda just said that in the first place."

"I get carried away sometimes."

"You really understand that high-level science stuff?"

Twilight chuckled. "Well, the eminent Dr. Feynmare once said that if anypony thinks they understand quantum thaumodynamics, that's proof that they don't. But I have a decent grasp of how it appears to function, and the math behind it. Enough to get a rough idea how much umph I'd need to break us out of here."

"You already tried the brute force method, though."

"Yes, but it was— unfocused, shall we say? Once, I watched a mare split a twenty ton boulder just by giving it a sharp kick in exactly the right spot. I'm hoping this place has got a hidden fault line or two."

Windfall nodded. "Sounds reasonable."

They worked side by side for several hours until Windfall broke the mutual silence. "Hey Princess, d'you think it'll be okay for me to go off into a tunnel for a little bit?"

Twilight blinked and shook herself, changing mental gears. "I'm not sure. Still no tunnel shift, and I think that means our maniac is thinking things over. But that doesn't mean they might not take the opportunity to seperate us for some reason. If you want privacy, you could go behind the big boulder over there."

Windfall chuckled and held up her finished instrument. "That's not nearly far enough away! These things sound weird enough when they're in tune. Getting one into tune is an ordeal for anypony in earshot."

Twilight gave her a smile. "Don't worry about it. I'm pretty good at focusing on a task. Too good, some ponies have told me."

Windfall looked doubtful. "If you say so…" She trotted off to the other side of the big rock.

Three minutes later, she looked up to find Twilight standing over her, wide-eyed and twitching. "Is that an instrument of music or torture?" she half-shouted.

Windfall laughed. "Told ya. It'll sound a lot better when it's tuned up, I promise."

"I learned to ignore my brother trying to murder a violin for three months, but this—" Twilight shook herself as if she were trying to dry off after a swim. "How does it make such horrible noises without dark magic?"

"Three tuning pegs per string, and they screech like banshees if all three ain't exactly right."

"Wait… what? Three? Strings only have two ends and only one needs—"

"Nope." Windfall shook her head. "Not these strings, Princess. See? They split about two thirds of the way down from the neck. Both ends of the 'legs' need to be tensioned exactly the same, and the 'body' needs to balance them both in harmony." It was kind of nice for her to be explaining something technical to the alicorn instead of the other was around for a change. "Each twist of a peg usually throws off one of the others, so you've got to go back and forth a whole bunch to get them sounding right."

"Recursive," Twilight muttered under her breath as she stared at the strange instrument in fascination.

"Yeah, that. But, being able to play two different notes on one string at the same time is worth it. You can get—"

"Get one of the strings in tune and let me measure it!"

"Uh… Sure thing, Princess," Windfall said, surprised at Twilight's sudden intensity.

Twilight didn't take her eyes off of Windfall as she worked, but her horn lit, and her notebook and measuring stick came floating around the boulder.

Once one of the strings was sounding "right" (Windfall refused to use the word "good"), she let Twilight take the measurements and then went back to tuning the rest of the strings. To her amazement, Twilight did seem to be able to ignore the ghastly screeches and buzzes that the untuned litungkano produced.

Windfall finished to her satisfaction and began playing a tune. She didn't consciously pick one, but found her hooves moving to an old Zebrican lament she'd learned in the Mareghreb highlands.

She came to the end and let the last buzzing note swirl away, uncertain that all the effort had been worth it. The music was good, even comforting in a way, but the memories it brought back…

"That was— strange, but in a good way. Exotic," Twilight told her. "Almost as if wasps had learned to sing choral music. It's like no other instrument I've ever heard."

Windfall nodded. "It's an unusual one, alright. Even a lot of the zebs don't like it. Sorta like Earth Ponies and bagpipes. They either love it or hate it."

"I think I know why it sounds so bad when it's out of tune," Twilight said, holding out her notebook open to a two page spread.

Windfall glanced at the complex diagrams that crowded the pages. "Why don't you explain it to me?"

"I thought at first the leg portion of the strings produced one note and the body part another, but that can't be it. I think the legs subtract from the harmonic length of the body, but only in one dimension! They prevent the body portion from vibrating horizontally from where they join in, but the whole string can still vibrate vertically at a different wavelength. So when it's out of tune, the disharmony is literally trying to tear the string apart!"

"Huh. Yeah, it kinda sounds like that, doesn't it?"

Windfall wasn't all that interested in why her instrument sounded and behaved the way it did, but Twilight was having so much fun explaining frequency, amplitude, and fractional harmonies to her that she let the alicorn ramble on for several minutes. And she found that, after a while, she understood the phenomenon pretty well.

"So… putting another set of legs at the top of the string wouldn't do anything, right?"

"It might, but it would be an order of magnitude more difficult to tune!"

"But that sketch you did of a third leg… where'd that notebook go?" Windfall scooped the little book up off the ground and riffled through the pages, stopping at a mass of wavy drawings. "Let's see… I think it was… no, these look different."

Twilight glanced over her shoulder. "Oh, those aren't about the litungkano strings, those are thaumic waveforms."

Windfall frowned down at the page. "They look pretty similar."

Twilight chucked and shrugged. "Everything is made of waves of some sort. Light, sound, electromagnetism, magic, even matter. Teeny-tiny waves of probability. If it wasn't, there would be no way to transform anything."

"You're pulling my leg, right?"

"Not at all! I never joke about science!"

"So what's the magic equivalent of this?" Windfall plucked the lowest string on her instrument hard enough that the echo from the cavern added interesting subtones to the sound. "Black magic?"

Twilight laughed. "No, and the term is dark magic, 'black' is considered…" She trailed off, her eyes lost focus, and her jaw dropped open ever so slightly.

Windfall frowned. "What's up, Princess? You have a stroke or something?"

Twilight ignored the mercenary, and grabbed up her notebook and pencil in her magic and began furiously scribbling away.

By then, Windfall was used to this sort of behavior from Twilight and shrugged it off. She went back to strumming the litungkano, working her way through all the old songs she could remember.

Twilight Sparkle kept working in a frantic rush of thoughts and ideas, until she produced one simple and elegant formula that absolutely terrified her.

Author's Notes:

The litungkano is a portmanteau of two different Kenyan instruments, neither of which have Y-shaped strings.

Some people have experimented with such strings, and the physics and sound is pretty much as I described above. Unless you're a fan of bands like Einstürzende Neubauten, you probably wouldn't enjoy listening to a Y-string guitar, but it is an amazingly unearthly sound:
Litungkano
(Not quite as buzzy and weird as the guitar strung this way, but it'll give you an idea. Filmed under the 2020 California/Blade Runner sky, which is why it's so yellow, and you can hear me wheezing through my mask.)

And, thanks to Nachtschwalbe, we now have another example of a Y-stringed instrument:
Tritare
(This one has a lot more reverb and less buzz than I remember, but it gives a good idea what an entire instrument strung this way would sound like.)

N.B. From the Wikipedia entry on the tritare: "Richardson also claims that the tritare sounds bad."

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Thanks to Archangel of the Silent for a great editing job on this chapter.