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"Severus…"
No, Dumbledore. I cannot do it.
Dumbledore had asked it of him as a favour. A favour! Did he not understand just what it was he asked?
You alone know whether it will harm your soul to help an old man avoid pain and humiliation…
But that wasn't it at all, damn him! Had he forgotten just what was needed to cast the Killing Curse?
"Severus… please…"
Unforgiveable Curses required more than the correct incantations and wand movements, more than an understanding of the theory behind them. You had to mean them. You had to want what you knew would result. You had to hate.
Damn you, Severus thought. I respected you. I loved you! You gave me a second chance when no one else would. How could you make me do this? How… could… you…!
"Avada Kedavra!"