The little darling is still winded from your last blow, you doubt she'll be up anytime soon, but you don't want to take any risks. While she's still down you retrieve your "Med Kit". It's an adorable little thing, given to your by your mentor as a present for successfully vivisecting for first pony years back. You still have your mother's skull and a few teeth in it to remember the occasion.
You flip it open with your hoof and grab a long, thin saw between your teeth. Fluttershy was finally coming to, so you quickly jumped on top of her. Fluttershy yelps as you slam on her belly with your rear, knocking the wind clean out of her lungs. She would struggle, but she doesn't want to upset you.
"Uh, um, excuse me," She says, but her protests go unnoticed. You lean down, saw in mouth, and begin to tear away at the flesh of her haunches. Fluttershy cries out, but she seems to be holding back. You move your neck faster, cutting through flesh and sinew, until you reach her bone. You turn around to check on your patient, but the little pegasus is only biting her lip out of pain, a few tears lining her eye. You'll fix that.
You slam down your hoof on the joint, and a crisp snap sounds out, just like a twig broken underhoof. Fluttershy screams, and a pulse of blood spurts out of the ruined stump. You turn to the other, but drop your saw. You want this one to go faster, and a thick bladed cleaver will do much better. You rear upwards, then swing the edge down onto her remaining backleg. The heavier blade gives a much deeper cut, on your next hit you're already at bone. One more swing and you snap it, although it wasn't as clean as the last one.
You drop the cleaver and grab her hoof, still attached by a few muscles and bone fragments, and pull. Fluttershy screams her lungs out as you pull, a sickening stretch followed by gristly tear, as more gore splatters out onto the floor, which is now almost exclusively red. Drat, she'll bleed out soon, and you can't have her dying yet.
From your box of wonders, you grab a small blowtorch, quickly igniting it against Fluttershy's stump. She moans, her throat is probably too sore to shout anymore. The smell of singed flesh and burnt hair smolders over the room as the wounds are filled with clumps of doughy flesh. Messy, but effective.
You look to Fluttershy, her face is an agonized mask of pain, drenched in sweat and pulsing with her struggling breath. Mm, that face and the fresh blood on your hooves is driving you wild. Time for the next procedure..