"Most people called them "hybrids." Rose's father, David, called it a "condition." An illness, a disease. For forty-one days out of every six weeks, she looked human, For that terrible, final day, she was...nothing, Not human, at any rate, Not sane either. Her normal self - her human self - had no control over what she did. She was a creature of pure magic, and she was programmed to kill. She was fifteen years old. And she was a monster" -- Jacket.
