She'd grown attached to the sound of buzzing flies.
Take that, as you will.
Once you've been around something, it's hard to rid yourself of habit. Her's just happened to be around rotting decaying flesh and fur, which brought many bugs nourishment. it did nothing to stop the flops her stomach turned within her. She'd never "dissected" something before. It seemed cruel, just to open up another creature for study. Although this one seemed to pay no mind. It's head twisted this way and that, trying to free itself of the binds. Saliva glistened on it's teeth, and it let out a low snarl that exposed it's gums, rotting away just as the corpse itself.
It took everything within her not to vomit at the sight. This, was something she would not get used to. She brought her thoughts back to the buzzing insects, taking solace in their low hums. She internally wished for cleaner sterile equipment. The pony underneath her makeshift binds made no changes in it's violent behavior, throwing it's head back onto the table, with a slick thump that made Twilight cringe. The bodies got softer, as they decayed. She wondered how badly it's cracked it's skull, as that seemingly had gone just as soft.
Not enough, to kill it hopefully. Not that she had much to worry about, as almost little to nothing could kill the ponies that had come from the disease. Only to where the brain was nonfunctional, and the table had certainly not been that hard. She gave a nervous chuckle, that she quickly silenced. This wasn't a laughing matter.
She stared down quietly at the intestines. They were a light gray, and many of them had "imploded on themselves". The waste they had been holding previous were scattered throughout the body, littering it with more and more filth. She felt a disgusting taste in her mouth, and turned away from the sight. It was too much.
There's nothing to fix.
She took a needle and thread, and began to sow up her previous incision. There was no helping them, now. She turned to the pony beneath the binds, thrashing and moving it's hooves to reach towards her. The previous white fur was now a light gray, dotted with small bits of crimson. The perfectly curled mane had been completely removed, only small patches of purple left on the scalp.
Twilight bit her bottom lip, and let her horn glow a pure magenta.
"It'll be over soon, Rarity." She whispered, more to herself than to her friend.
The door behind her creaked, and she heard a small gasp of fear and pain. She ignored it. There were things she had to do. She slowly levitated an icepick above the unicorn's forehead.
"Goodbye, generosity. You were generous, until your last breath. Giving your body to science." Her bottom lip quivered, and tears rolled down her cheeks.
Then, in an instant, the unicorn's eyes were blank as blood pooled from her cranium. It was quick, and it was painless. It was what she would have wanted.