"Obsessed? I don't know what the word means. I know there were times when I couldn't think of anything else. I used to stay in every weeknight in the hope that he might get free and call me. It felt like I had a disease I didn't want to get rid of. I suppose that's a definition of obsession, yes."

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Kill me then,' panted Harry, who felt no fear at all, but only rage and contempt. 'Kill me like you killed him, you coward-' DON'T-' screamed Snape, and his face was suddenly demented, inhuman, as though he was in as much pain as the yelping, howling dog stuck in the house behind them- 'CALL ME A COWARD!

— J. K. Rowling