They all learned about anatomy when they were younger. Donnie gathered them in the living room, Splinter sitting ideally by with a soft smile and tea in hand while the others groaned. They learned bits and pieces of the human anatomy and the turtle anatomy. It wasn't like anything was set, it was either or but necessary. Crude humor would constantly interrupt Don and it was mainly from Raphael. Mikey was close to joining in with his brother until Raph earned himself a firm strike from Master Splinter's tail. But yes, they did learn everything. Everything. Even the important bone structure and what their shells were made of.
Mikey innocently believed cartoons and comics theory of a shell just being a home. Regular turtles were able to hide in them for protection and predators. They couldn't due to their size and their heads being too big to fit. They were able to when they were smaller, Splinter reminded them, but now they simply were protection.
And were awesome sleds during the winter.
He would never get use to the sight of seeing the inside of one. His eyes saw the bone, blood, tender raw flesh that bled at a touch and died. Leo couldn't stomach the sight anymore than the rest. Not when it was his brother. The one who taught him everything about their bodies little by little. The one who showed everyone how to correctly stitch wounds and mend a broken bone. Donnie sucked in all that information from books he found in sewers, taught himself how to read and processes all that knowledge. It was all for them and for their survival.
This was something he had no clue how to mend.
Donnie had been near comatose whenever Leo would clean his shell over and over. If April was there to help, they would get rid of the dead flesh that began to grow along the inner walls of the wound. April had a stronger stomach. After a few minutes, Leo's hand would shake and he would excuse himself. It wasn't fair. He failed to protect his little brother, he abandoned him, and now he couldn't save him. The chances of him pulling through were slim and even if he could Donnie just wouldn't be the same.
Leo spent the rest of the afternoon alone in Donnie's room. After finishing up the new bandages and giving Donnie two more strong sedatives, Leo sat beside him in silence. His hand rested on top of Donnie's and gently rubbed his thumb along Don's wrist. He wasn't asleep. Leo picked up the heavy breathes and soft groans from his brother. After seventeen years, Leo knew Donnie would whistle in his sleep and occasionally talk. How he wished to hear something familiar from his brother. Something that would give him a sense of hope that he so desperately wanted to cling and hold on to.
"Please.. tell me how to fix this.."