Alphys's tests weren't like puzzles. Unless the puzzle was "how long can you be still and not pick at the weird suction cups while this big machine spits out boring graphs."
In which case the answer was five minutes and twenty-two seconds.
"SANS, CAN YOU CHECK MY POCKETS? I BELIEVE I LEFT A JUNIOR JUMBLE IN THERE FOR EMERGENCIES." Papyrus started to swing his stubby legs back and forth, but the wires connected to the machine held them in place.
"Sure. Be good for Doctor Alphys while I'm gone, little bro." Sans winked before ambling out of the lab.
Papyrus grumbled and gripped the armrests of his chair. Of course this whole mess wasn't bothering Sans. Nothing ever bothered Sans! How could he always stay so calm and collected when Papyrus just wanted to scream?
"I-it won't be much longer," Alphys assured him. "I know what I'm looking for from Sans's data."
Sans had woken up hours before him, so Alphys had run his tests first. Papyrus couldn't remember a time Sans had been awake before him. Something must be wrong with this body. Maybe Alphys could figure that out while she was running these other tests.
"WHAT ARE YOU LOOKING FOR, EXACTLY?"
"U-um. So you know how each monster's magic has a different pattern of vibrations, right?" She went on without waiting for him to answer. "The magic that makes up our bodies, I mean. Those vibrations allow our dust to take up more physical space while having less matter than humans. It's like each dust particle occupies more than one point in space at once, and… w-well, that's not so important."
"IT IS INTERESTING, THOUGH! I DIDN'T KNOW ALL THAT."
Existing in more than place at once… that almost sounded like Sans's shortcuts. Maybe Alphys would be more helpful in explaining how they worked. Sans always shrugged and said it was "just something you feel in your bones."
"W-well!" Alphys smiled. "The vibrations! Yours—your body's, I mean—seems to have a much higher frequency than Sans's. I compared your body's pattern to that of the older bone attacks you've given me, and they seem the same. Which means your body's structure wasn't damaged when you and Sans switched."
"THAT'S GREAT!" Papyrus grinned. "THAT EXPLAINS WHY SANS CAN'T SHORTCUT NOW, TOO. HIS MAGIC STAYED WITH THIS BODY, RIGHT?"
"I… u-um." Alphys looked away, focusing back on the machine's monitor. Papyrus couldn't see it from his chair, not that he would've been able to interpret the graphs anyway. "I'm—I'm not sure? I didn't want to scare him while he was here, b-but maybe you can help me. He… his body… i-is it always so…?"
"LUMPY? ROUND?" Papyrus's brow furrowed. "FRAGILE?"
She looked up. "L-like… one HP fragile?"
"YES! SORRY I DIDN'T TELL YOU. I THOUGHT YOU KNEW."
He'd known about Sans's condition his whole life, but Sans hated making people worry. Of course he wouldn't have brought up his health, even when it was important.
"I didn't. But that explains these readings. His magic's frequency is… w-well. I didn't know a monster could survive with a frequency that low. When he told you to be careful with his body, he was actually being serious." She sounded surprised by the realization, but Sans could be serious. He just usually bookended any sincerity with jokes.
"I CAN HANDLE IT, DOCTOR ALPHYS. AFTER ALL, I HAVE BEEN TAKING CARE OF SANS PRACTICALLY AS LONG AS HE'S TAKEN CARE OF ME! I'M GOING TO TAKE SUCH GOOD CARE OF HIS BODY, HE WON'T EVEN RECOGNIZE IT! NYEH HEH HEH!" He flexed his arms.
"P-please don't tug on the nodes." Alphys rushed to reattach one of the suction cups to his humerus.
"OH. SORRY." He moved his hands back to his lap. He missed his gloves, but they were too big for his now-tiny hands. He tried to mimic the comforting texture by balling his fists in the soft fabric of Mettaton's tour shirt.
It wasn't the same.
"Anyway. It might not be that simple," she said while tapping her claws against the keyboard. "Regular training can improve attack and defense, but HP is tied directly to the soul's frequency. The only way I know of to change that is by increasing, er, LOVE."
"YOU MEAN I CAN LOVE MY BROTHER INTO INCREASING HIS HP?" he joked. Alphys didn't seem to get it, though. Maybe he should've added an audible wink.
"N-not exactly. He would need to—"
"I KNOW, DOCTOR ALPHYS. AND HE WOULD NEVER DO THAT." Papyrus frowned. "YOU SAID HP IS DEPENDENT ON THE SOUL?"
"Yes. The higher the frequency, the higher the HP. Frequency doesn't seem to affect anything else, though. Attack and defense are dependent on amplitude and wavelength, respectively, which can each fluctuate with a monster's emotions—"
"WAIT." His eye sockets widened. "IF I'M IN SANS'S BODY, AND HIS BODY HAS ONE HP, AND HP DEPENDS ON THE SOUL—I HAVE SANS'S SOUL?"
"Oh." Alphys's face reddened. "I w-was supposed to break that more gently. But, um, that's what the data suggests. I don't have a control group for his magic, since he's never, um, given me any bone-gifts…"
He barely heard her over the sound of his screaming.
"HOW CAN I STILL BE ME AND HAVE MY BROTHER'S SOUL?" He clutched at his chest.
He was still him. He remembered everything he'd done yesterday. He'd arranged the resort staff's schedules, calibrated the mini golf puzzles, taken his car for an oil change, and, of course, tried to pick up Sans from Grillby's.
"That's where things get confusing." She sighed. "I'm doing my best, here. But souls… no one's ever figured out exactly what they are. We call them the culmination of our beings. We say they're made of love, hope, and compassion. They have frequency, wavelength, and amplitude like a wave, and yet they react with dust to give our bodies the illusion of a physical form. They're magic that can produce more magic, either in the form of bullets or of offspring! Monsters are thousands of years old, and we still don't even know how that works!"
Papyrus blinked as she tugged on her spikes.
"UM. WOULD HAVING A BABY PUT MY SOUL BACK TO NORMAL? OR IS THIS ONE OF THOSE METAPHOR-PUZZLES…?"
"S-sorry. I get a little carried away with this stuff." She adjusted her glasses sheepishly. "I'm only the expert on monster souls by default. And I just—I wish I knew more. If I did, maybe I could answer your question. But the truth is… I just don't know."
She sat back in her desk chair, and her tail curled around her legs. She… she really was trying her best. She always did.
He felt the lights in his eyes dim. He was being an awfully poor Compassion Coach right now.
"IT'S OKAY." He reached his arm as far as the little suction cup would allow. It wasn't quite far enough to pat Alphys's knee, but she politely scooted closer. "YOU DON'T HAVE TO KNOW EVERYTHING. YOU, AND ME, AND SANS—WE'LL FIND THE ANSWERS TOGETHER! AND IT SOUNDS LIKE THIS HAS ALREADY TAUGHT US SOME IMPORTANT FACTS ABOUT SOULS, RIGHT?"
"R-right!" She sat up a little straighter. "L-like, before now, I thought that a monster's consciousness would be tethered to their soul! Except in unique cases like Chara and Flowey! But now we know that consciousness can be transferred independently, which opens up a whole realm of possibilities! Maybe I can even—"
She pushed off of his chair with her tail, rolling herself back to the computer. A flurry of clicking came from her keyboard.
"MAYBE YOU CAN WHAT?"
"If I can fix you and Sans, then there has to be a way to save them!"
"You don't think we're getting a bit ahead of ourselves?" Sans strolled back into the room. One of his gloved hands held Papyrus's Junior Jumble book. The other held a smoothie, which he slurped loudly.
"SO THAT'S WHAT TOOK YOU SO LONG!" Papyrus scowled. "...CAN I HAVE SOME?"
"Heh. Knock yourself out." Sans set the puzzle book on the table beside him, then passed him the smoothie.
He took a big sip—and choked when the clashing flavors of mango and mustard hit his mouth.
"SANS! MUST YOU RUIN A PERFECTLY GOOD BEVERAGE WITH YOUR STRANGE CONDIMENT ADDICTION?"
"Only if I know you're going to ask to try some." He winked and took the smoothie back. "MTT made the right call on installing that smoothie bar. You should tell him thanks for me."
"I DOUBT HE PUT THE MUSTARD THERE! HE HAS STANDARDS!"
"Nah, that was me. He did leave a nice stockpile of edible glitter, though." Sans went back to drinking the smoothie like it wasn't pure poison. Honestly, it was a miracle he didn't lose his one HP from his awful eating habits. At least the fruit was a step in the right direction.
Of course, since he was in Papyrus's body, it wouldn't affect his health either way.
"Was he good for ya, Al?" Sans asked.
"Papyrus was great, as always." She gave him a sincere smile. "He helped me piece a few things together. I'm ready to share my preliminary hypotheses."
She finished her typing and ripped a graph from the printer. Papyrus took that as his cue to remove the pesky suction cups.
Under Alphys's recommendation, they took the escalator up to the living room. Papyrus grabbed a non-tainted strawberry smoothie on the way. The smoothie bar was a great idea. Of course, his boyfriend always had fantastic ideas, even if he usually needed help implementing them. Papyrus was always happy to help with that part.
"So is it good news or bad news, doc?" Sans crossed his leg over his knee as he reclined on the couch. He was still wearing the MTT-Brand Hotpants he'd borrowed. Even if Papyrus wished he were wearing them himself, he could at least appreciate that they looked good on his body.
"W-well. This is only the first batch of tests. There's only so much the wave analysis can tell us, but so far so good? I think?" She cleared her throat and spread her graphs across the coffee table. One showed a wave that spiked up and down in a rhythmic pattern. The other was nearly a flat line, only disturbed by a few small bumps.
She pointed to the first graph.
"This is your current magic reading, Sans. That is, it's Papyrus's body's magic." Then she pointed to the second one. "This, um, is Papyrus's reading. Sans's body. Papyrus told me that these readings are, um, normal? For you?"
Sans sighed. He set down his smoothie.
"Heh. Can't get anything past you two, huh?"
"IT WASN'T A SECRET, WAS IT?" Papyrus's browbone creased. "IF IT WAS, YOU CAN'T HIDE IT FROM YOUR DOCTOR! HOW IS SHE SUPPOSED TO HELP IF SHE DOESN'T HAVE ALL THE FACTS?"
Sans tugged at his collar. "Right… sorry. Just didn't want to worry ya."
"It's okay. The important thing is, we know your bodies are both stable." A drop of sweat beaded on Alphys's forehead. "I saw no change in your soul readings over a forty-five minute period, which would have been long enough to show any signs of decay. And Papyrus's magic was identical to his control group. Sans, I didn't have a control for you, but if this looks normal—"
"It is." His voice was flat.
"R-right. Then I don't think we have anything to worry about, short-term. Um." She swallowed. "So I bet the big question now is, how are we going to get you guys back to normal?"
"RIGHT!" Papyrus looked back and forth between his brother and his friend. "AN EXCELLENT PUZZLE, WHICH I AM WILLING TO FACE WITH ALL OF MY WITS!"
"Great. What's your bright idea?"
Sans sounded tired already. That didn't make sense. They shouldn't both feel tired. Papyrus was doing an excellent job of pushing through it though, if he did say so himself.
"WELL!" He clapped his hands together. "I SAY WE ASK DOCTOR ALPHYS FIRST, BECAUSE SHE IS THE BRILLIANT EXPERT! AND THEN WE TAKE TURNS GIVING IDEAS, NO MATTER HOW RIDICULOUS THEY MAY SEEM! THIS IS AN UNPRECEDENTED PROBLEM, WHICH REQUIRES AN UNPRECEDENTED SOLUTION! NYEH HEH HEH!"
Alphys blushed a light red. "Thanks, Papyrus. Um… I think the next step would be to conduct another experiment. You can both use blue attacks, right?"
Papyrus looked at his brother and grinned.
"IN THE FIELD OF BLUE ATTACKS, WE'RE THE CREAM OF THE CROP!"
Sans chuckled at that. "We'd be happy to show off the fruits of our labor."
It was an inferior pun to Papyrus's, but seemed to put some enthusiasm back in his voice.
"Great." Alphys grimaced. That was a pretty standard reaction when hit with back-to-back puns. "I was thinking you should try passing one attack through another. Then we can test if the attacks' frequencies change."
Sans nodded. "We got ourselves scrambled by passing through the same space at the same time. Guess this could mimic that on a small scale."
"I'M WILLING TO TRY IT!" Papyrus leapt up from the couch, but overestimated the length of his legs. He ended up stumbling into the coffee table and sloshing smoothie onto Alphys's reports. "UM. OOPS?"
"Don't worry. Not the first time I've gotten food on my lab reports." Alphys scooped them into a nearby trash can. "I'll just print out a new one. But, um, bones are a little harder to clean up, so let's go outside before testing this next—"
"AUNT ALPHYS!" Chara's voice echoed from downstairs. "FLOWEY AND I ARE HERE FOR THE SCIENCE STUFF!"
Alphys's eyes widened. Then she said a word that should not be repeated around the children.
"Swear jar." Sans grinned, but sweat collected on his forehead. "Don't you ever lock the door?"
"Undyne and Mettaton broke it down too many times." She covered her face with her claws. "I totally forgot I told Chara and Flowey to come back today. I'm not ready for them, they're going to be so disappointed…"
Why were they suddenly nervous? The children of all people would understand the struggle of being stuck in the wrong bodies.
"OH, AND MOM'S HERE FOR UNCLE PAPYRUS AND DUNKLE SANS!"
Sans blushed red. That was new. Was he finally starting to acknowledge his feelings for Toriel?
"WELL, LET'S NOT KEEP THEM WAITING!" Papyrus dashed for the escalator.
"Wait, Paps, don't you want to—" Sans called, but he was already on his way down.
"I WANT TO SEE MY FAVORITE NEPHEW AND NIBLINGS!" He did force himself to take the escalator slowly, though. He wouldn't want to trip or get his socks caught in the mechanical parts. He couldn't wait to get his feet back into some properly supportive boots.
"Sans, you've outdone yourself this time," Sans sighed to himself behind him.
"OH, STOP BEING SUCH A DRAMA QUEEN! I'LL EXPLAIN EVERYTHING ELOQUENTLY AND SUCCINCTLY, SO YOU CAN BE AS LAZY AS EVER!"
He stepped off the escalator in time to see Chara, Flowey, and Toriel all staring at him.
"Is this some kind of joke?" Flowey grumbled in Chara's arms. "Where's the doctor?"
"Heh. It's some kind of joke, alright." Sans's forehead was dripping so much sweat, some of it fell on Papyrus's skull. Just one more wonderful part of being the little brother.
Toriel's eyes widened. Flowey's tiny jaw dropped. Chara started laughing, and laughing, and laughing.
"Papyrus, are you feeling well…?" Toriel stepped forward. Towards Sans.
"OVER HERE!" Papyrus waved helpfully. "I KNOW I'M MUCH HARDER TO SEE AT THIS HEIGHT. BUT I'M ENDURING THIS AWFUL STATURE QUITE GRACEFULLY!"
"Papyrus—Sans—?" She pointed back and forth between them before her hand covered her mouth. "Oh dear."
"Understatement of the year, Tori." Sans chuckled nervously.
"Man," Chara said when they caught their breath. "This is gonna be so much fun."