Pink eyes scanned the computer screen again and again, the brilliant mind behind them trying- and failing- to comprehend the new information he was being given from the genetic analysis.
His own genetic report was nothing particularly special or surprising- his base DNA was that of an amelanistic Mus musculus, with additional strains of genetic coding taken from a variety of species and spliced into his own genome to produce who he was today.
On the other hand, Pinky's report…
He looked over at Pinky, currently running on his wheel as happy as could be. His gaze fell to his back and limbs, both substantially longer than his own- a fact that he had now, for the longest time, assumed had been simply him comparing his own relatively diminutive stature to his cagemate's. Now, however, it only served to corroborate what the computer had revealed.
Pinky. It couldn't be, he was a fellow lab mouse- a Mus musculus like him, perhaps with some different genetic inputs but like him all the same. There had to be a mistake.
He glanced between the computer monitor and Pinky a couple more times, still trying and failing to rationalize this in his head, before, with a deep sigh, walking over to his friend to confront him.
"Pinky."
Pinky looked over at the Brain and smiled, lifting a hand and waving it- before immediately tripping over and getting spun around by the momentum he had built up in his wheel. He stood up wobbly as it came to a stop, shaking the dizziness from his head. "Oh! Hello Brain! Narf! You finished tonight's plan to take over the world?"
"Ah… no, Pinky," he muttered, unusually subdued. "But there's a more… pressing matter that we need to deal with right now."
"Egad!" The taller rodent gasped, raising a hand to his face in shock. "More pressing than taking over the world?"
"Yes, even more pressing with that- come, Pinky, we have much to discuss."
Pinky followed obediently over to the computer, plopping down in front of the keyboard as the Brain bounced quickly across the keys, bringing up a chart with a picture of him in the corner.
"Pinky, as you know, I am an amelanistic member of the species Mus musculus- an albino laboratory mouse, in layman's terms, as defined by my white coat, red eyes, small stature, and completely furless tail- traits you too, Pinky, share. However, it doesn't take a genius to see that, between us, that's where our similarities end. Now, hold your arms out for me for a moment."
"Like this?"
"Perfect. Hold still."
The Brain hopped off the keyboard, grabbing a small tape measure from off the desk and starting to measure Pinky, his ears drooping lower as he wrote down each measurement, a detail that didn't go unnoticed by the empathetic Pinky. "Did- did I do something wrong? Poit."
"No… but tell me, were your parents of a similar height as you?"
"Well… I suppose so, we've always been a bit of a tall bunch, Zort, well except for my little sister-"
"Taller than the other mice around you?"
"Why yes! Much taller!"
Brain sighed, putting down the tape measure. "Then it seems your genetic report is correct, Pinky- you're not a lab mouse at all, you're not even a mouse. Look."
With that, he clicked out of his own profile, bringing up Pinky's report in its place.
Project B. R. A. I. N. Subject 2
Age: 2 years, 3 months
Core species: Rattus norvegicus domestica
Pinky's brow furrowed as he read through the report, the large words getting him all confused. "Brain… what's a Rate us norveggiecarrots domesticated?"
"Rattus norvegicus domestica is what you are, Pinky, not Mus Musculus like I. Rattus norvegicus domestica… is the Domestic Rat."
"Naaaarf… But wait, no I- I'm a mouse! Not a rat!" Pinky mumbled, failing to put the pieces together in a way that made sense. "If I were a rat I'd be all- all big and rat-like!"
"Pinky, you are big and ratlike."
"But- but-" Pinky's eyes welled with confused tears, a waver in his weakening voice. "But I'm not a rat! I'm a mouse, like- like you!"
Brain felt a rare pang of empathy for his associate- the shock he'd felt upon this realization had to be a hundred times more intense on the other rodent.
"Pinky-" he shouted, grabbing a hold of his shaking shoulders to ground him. "I understand that this is quite a thing to come to terms with, but being a rat is not a negative thing. Sure it- it probably explains our behavioral differences, as well as our- well- physical ones, but it doesn't mean you're any different in my eyes. You're still my cagemate, and you're still my friend."
Pinky sniffed, feigning a smile and wiping away his tears. "Really brain?"
Brain did his best to give him a comforting smile, patting him on the shoulder. "Yes Pinky, really."
He quickly found himself pulled into a vice-like hug, the taller rodent rubbing his cheek against Brain's own. "Oh, thank you Brain! Zort! That makes everything so much better when you put it that way!"
The Brain simply grunted as he pulled himself free of Pinky's arms, taking a deep breath as his lungs decompressed. "Yes, well, with that manner of business taken care of I suppose it's time to plan for tonight."
"Why Brain?" Pinky puzzled, following his mousey companion. "What else are we doing tonight?"
"The same thing we do every night pinky- try to take over the world!"
Et Voila, my first foray into this fandom! Honestly, this all started as an inside joke between me and my friends about Pinky's height making him believably a rat. I know Canon may argue differently, but that's why this is fanfiction i suppose :P