Demon (Warning, It's Gory)

This is one of the writing exercises we had in class. This one, specifically, was based off a mix of Buffy the Vampire Slayer and Jennifer's Body, at least in the idea of demons and how they act. All I want to know about this story is how I could make it better, make the characters clearer, or how I could just expand the story idea. Also, I'd like to know which line was your favorite, and why.

Her teeth hurt. The sharp pain in her jaw made her whimper and she rubber her mouth. Biting down, harder with every second to try and ebb the discomfort, Sabrina closed her eyes. When nothing worked, she made her way across the hall from her room to the bathroom to look in the mirror.

She opened wide, inspecting her teeth. No cavities, she thought. She touched a finger tip to each of her teeth, beginning at the back of the bottom row and then going against her upper jaw. At her canines, she flinched. Looking down at her finger, a bead of blood began to well up. She sucked on it, never before realizing how delectable blood could taste. She looked back in the mirror, opening her mouth again. Her teeth were longer, sharper, resembling those of Venom from The Amazing Spiderman. She let out a cry of terror.

"Sabrina!" Misty, Sabrina's twin sister, appeared in the doorway. The terror that decorated Misty's face was unforgettable. Sabrina smiled, her teeth showing in all their pointed and fearsome glory. "Bri... what's going on?"
Sabrina walked over, carefully taking her steps at a pace to keep Misty from running. Her twin stood, frozen in an awe that could only be conceived by a mix of fear and previous admiration. She reached out, putting a finger on Misty's exposed shoulder. She slid the tip of her nail down her sister's arm, an almost intimate gesture if it hadn't been for the now razor-sharp tips of Sabrina's nails slicing open the fragile skin in a line of red fury.

"Bri-" Misty was breathless as her sister's hand came up to the nape of her neck, her claws piercing into the flesh there. "Don-" Misty could barely make out the word before Sabrina brought her mouth to her throat. A gurgle of fear mixed with blood rose up in Misty's trachea. Sabrina's tongue played with the shredded muscle of her sister's neck, her senses delighting in the blood she had spilled.

Sabrina feasted until, between the flesh and the blood of her sister, she felt sated. She laid Misty's corpse in the tub, closing the shower curtains to give her sister some privacy. She didn't even want to think of their parents' reactions when they came home to see their daughter mauled to death. What she did think of, however, was her skin turning black like that of the man's who turned her this way.

"Ah, what hormones do to you..." Sabrina said aloud, knowing that no one was around to hear her. She thought of the way he had messed around with her, the way he aroused her into letting him have his way with her. And then her thoughts wandered to where he had bitten her neck, keeping his teeth there only momentarily before he backed off, the moonlight outlining his body gloriously. Sabrina had looked up, and his skin had gone black like hers did now. He had explained to her what would happen. He had described to her the hunger she would feel and the emotions that would overcome her. The one thing he had never told her was how she would lust for the blood of others.

Hunger surged through her again, but this time her skin did not turn to normal. Maybe, she thought, Maybe that's a learned trait.

She moved swiftly out of her home, making her way through the front door and into the crowded main street that she and her family had lived on for as long as she could remember. Neighbor's whose children she had babysat stared at her in fear. Girls she had known since grade school ran away at the first sight of her. Men and boys looked at her, some of them seeming to be deciding what to make of her.

She looked herself up and down. Her naked body was black, but smaller than it had been before and she reminded herself of Raven from X-Men. Except that Raven was blue and Sabrina's hair wasn't orange, but it still wasn't hard to see why they stared.

Sabrina paused, hearing sirens of police she didn't know were contacted, and then she thought of her dead sister in the bathtub. The sister she had murdered. Memories flashed of birthdays and Christmases, filling her with grief. As the SWAT team came out of their trucks, Sabrina looked them dead on, suddenly more than ready to accept her fate.