I really loved how they were both so excited about the intellectual challenge, and her thoughts as to why he was usually polite around her, and the fact she taught him a hospital grade protection charm for his hands.
I LOVE THAT FILCH GAVE MRS. NORRIS A CHRISTMAS PRESENT. Man, I love him.
These are my favorite lines:
Severus stared at her for several moments, eyes strangely intense. Then he shook his head, averting his gaze. “No,” he said, speaking to the parchment in front of him. “No, I suppose I wouldn’t be.”
“Don’t you ever get lonely here in the castle?” His voice was earnest, this time, but not pleading.
I really love the plot of potions gone wrong like at the end. Well executed. And the ending is such a tease. :-) Very nicely done.