Tarsus trotted through the ever-changing corridors of the hive, pausing at certain junctures and walls as old openings shut and new ones opened, and even entire hallways realigned themselves. It was largely instinct that let him feel when and where the best routes through the hive are. Builders may have always had the best sense for how the hive shaped itself -something they had made into a point of pride- but caretakers were no slouches themselves. A lifetime spent in a place means you eventually find your way in it.
He paused in front of what seemed to be an empty wall, lightly tapping his hoof against the stone ground, "Four, three, two, o-" just before he finished, the sound of wet leaves being torn filled the corridor, and a hole opened up right in front of him. Tarsus allowed a small grin to cross his muzzle. "Almost."
Stepping through, the caretaker found himself in his latest workspace. It was an isolated space deep inside the hive, an open room with several large, green blobs of slime arranged in a crescent against the wall of the room. The bedpods each had one changeling lying on them. These were his patients, Last he had checked them, they had not been doing so well.
"How are they?" he asked Probos, one of his assistants, a green changeling with blue eyes who was currently scribbling notes down on a clipboard.
His assistant looked up from his work and scrunched his muzzle. "Worrying. While has been a few days, we're seeing an increasing decline in health the longer they are starved from love. Regular foodstuff seems to help, but only to a certain level. It can keep them alive, but it can't stop the hunger."
Tarsus frowned. "So we have been unable to find a substitute for love? What about the meat test?"
The changeling shook his head. "A bust. While it does seem to have a more powerful effect than regular pony food -in hindsight not surprising given our predatory nature- it still doesn't change the root problem: we need love."
Tarsus let out a long suffering sigh. "Let's run through the final analysis then. We've tried eating other emotions, which was a downright failure. We simply can't 'drain' emotions other than love."
"Historical notes suggest that there were other species that could. Sirens and Wendigo who fed on hatred and anger. Sirens maintain a threat to Equestria and are usually banished when they enter Equestria. The Wendigo... well, even we changelings know the tale of Hearth's Warming," Probos added.
"The war that was won without a single shot," Tarsus remarked. "So, not an option even if we could. Prince Thorax would never allow us to become enemies of Equestria. Next, we tried eating one's own love."
"Which also turned out to be impossible. We even had our hive's greatest narcissist give it a shot."
"I assume Mirrorshine took the disappointment with his usual grace and humility?"
"Last I heard he had started a quest for the first changeling alcohol to drink away his sorrow," Probos noted with a fanged grin.
"Noted. And second before last, we tried turning to regular pony food."
Probos flipped to the most recent page on his clipboard. "The initial results were promising. There was an initial recovery, and the body does seem to absorb the nutrients and remain alive. Meat proved to be even better at this, but after a certain peak was hit, we noticed a decline again. The body itself remains alive, but everything else just seems to... fade."
Tarsus sighed and rubbed his temple with a hoof. "We seem to have gotten all we can out of this experiment. If we cannot make any further progress, I am inclined to shut it down."
His assistant nodded, relief washing of him in waves. Tarsus raised an eyebrow.
A cough and Probos turned his head away, slight embarrassment tingeing his cheeks. "Apologies. I know I have assisted you with dozens of experiments far worse than this, but now... now I can't wait to end it, even though we could continue to gather every scrap of knowledge right up until the actual end."
Tarsus let those words run around in his head. What Probos said was right, they had done experiments far worse than this, but now that he thought back on them, he felt...
"Probos, do you remember our last experiment before Prince Thorax's return?"
The green changeling blinked. "That was the one where we perfected the magic sealant of our prison pods, wasn't it?"
Tarsus nodded. "That's the one. Now, I want you to think back on that experiment, and the subject. How does thinking back on it make you feel?"
Probos blinked, and Tarsus could see an uncomfortable look pass over the changeling, his eyes blanking slightly and the corners of his mouth dipping downwards. After a moment, the changeling furrowed his brow and shook his head. "I'd rather not. Is this relevant to our current experiment?"
Tarsus observed his assistant for a moment longer, but shook his head. "No. Not right now at any rate." Neither Tarsus nor Probos had had any problems with the experiment at the time, nor the poor pony that had been their subject at the time. But now, just thinking back on it... it made Tarus once again wonder just how much they had changed, and where it stopped.
Tarus shook his head. Probos was right. While concerning, the changes to their psychology were not directly relevant to the task at hand. He turned back to the bedpods to begin his rounds in earnest. One more check-up, if he did not find a breakthrough here, he would shut this experiment down.
Something told him Prince Thorax would want it that way.
Arriving at the first bedpod, Tarsus took a good look at the changeling. Spinner, one of the caretakers. His brown carapace had begun to lose its shine and his eyes had dulled.
"How are you doing, Spinner?"
The changeling tilted his head and smiled weakly. "Regretting volunteering for this. I feel like a pod gone bad. I'm hungry, tired, and even smiling seems like climbing the wall. The food doesn't seem to help much." A grunt that sounded like a chuckle bubbled forth from his throat. "On the bright side, I've found I really like fish, so yay for small things?"
Tarsus returned the chuckle and nodded. "We're nearing the end of this experiment. Just hang on for a little longer."
Another grunt, this one more of relief mixed with determination. Tarsus moved on to the next bedpod, and the next after that. So far, the results were as bad as he had expected them to be. The same symptoms, the same problems, all pointing to the same conclusion.
The last bedpod, his last patient. The worker he'd gotten to know as Scuttler was without a doubt the worst off. The poor changeling had looked underfed even before he had volunteered for Tarsus's experiment. As it turned out, Scuttler had refused to feed ever since the great change, even on the love that had been freely offered to him. When asked why, all Scuttler had done was look down, fear and disgust wafting off him like a forgotten nest with rotting eggs.
Approaching the bedpod, Tarsus noted that Scuttler had gotten even worse. His normally yellow chitin had lost almost all colour, turning into a light grey that seemed to be getting darker now. His normally red eyes had dulled almost entirely. "Scuttler? Can you hear me?" Tarsus spoke, unsure of whether Scuttler could even hear him anymore.
The changeling's head slowly turned until the eyes seemed to lock on to Tarsus.
"How are you feeling, Scuttler?" Tarsus asked.
"Hungry." The rasped response send a shiver down Tarsus's neck, and he involuntarily took a step back.
"How was the meat? Did it help any?" Tarsus had to force the questions from his mind to his mouth. The way Scuttler kept looking at him, eyes never blinking, never leaving his own, was unnerving.
"Hungry," Scuttler repeated. Now his tongue flared out and- did Scuttler's eyes just flash blue?
"I'll.. mark that as a no." Tarsus turned to his clipboard to mark the answer. This was insane, why was he even continuing this? Why was he letting this continue? "One last question, for the sake of finishing this properly, then we're stopping this. What are you hungry for?" The question was an obvious one, but asked after every new meal, just to see if something other than love had stuck in a changeling's palette.
Silence.
For one, brief moment, the question was answered with total silence. Tarsus looked up from his clipboard to see that Scuttler, despite his malnourished frame, had managed to crawl and turn to stand on his legs.
"...Love." The rasping voice finally replied. Scuttler was staring directly at him now, his tongue lashing out. "...Delicious love..."
"Scuttler? What's are you-"
Tarsus's words dried in his throat. Even as he was staring at him, Scuttler's dark grey carapace turned darker, until it became a dry black. His dull eye slowly turned blue. His wings dried until they started ripping.
An eerily familiar hissing sound rippled from Scuttler's throat. Then Scuttler lunged.