Disclaimer: I only claim the plot.
A/N: Non-canon. War is over, but my beloved Snape survived.
It was just another day in Double Potions with the Snakes. Hermione never thought she would be glad to see Professor Snape again, yet after viewing his memories in the Pensieve, she was overjoyed to discover he had survived. He may still be a cranky, Slytherin-favoring bastard, but knowing what she did about his feelings for Lily Potter plus his role in the War, Hermione had developed a bit of a soft spot for Snape. Not that he was discernibly friendlier to her or any other Order member.
The aforementioned cranky, Slytherin-favoring bastard had been called out of the classroom for a moment, so he missed it when Seamus Finnegan added too much chopped wormwood to his potion. Hermione saw the surplus just as it dropped in, and she called out, "Wait! Too much wormwood can cause-"
BOOM!
Too late.
In seconds, the Gryffindor muggleborn felt herself being tugged into a set of vise-like arms, and a pair of soft, warm lips descended ferociously on her own. She caught a flash of platinum blond hair before she closed her eyes and had the life snogged out of her. It was so intense she almost didn't notice that pandemonium had erupted around them.
A few moments later, Draco Malfoy pulled back from Hermione's kiss-swollen lips and glared at Seamus. "Damned idiot Irishman. Everyone knows the potential reaction when the Draught of Comprehension is brewed with too much wormwood." He glanced at Granger, then turned and walked back to his desk. The class focused their attention on Hermione, who shrugged. "He's right; there is a definite side effect." And she calmly returned to her cauldron.
The remainder of the lesson was as peaceful as it ever got in Potions, and she had just entered the Great Hall for lunch when it happened again: Malfoy appeared out of nowhere, and she was the victim of another kiss-and-run. This time, Professor Snape was on hand to witness the occurrence. He merely raised an eyebrow.
Ron was hysterical after seeing such an abomination for the second time in one day. "That's sick! It's wrong, and it needs to stop."
"Mr. Weasley, approach." Icicles dripped from the Potions Master's voice.
"Y-yes, Professor?"
"What happened in class today while I was gone?"
"Um, Finnegan used too much wormwood, and the cauldron exploded. 'Mione tried to stop him, but it was too late. Next thing anyone knows, Malfer...foy pounces on 'Mione and snogs her! They both said everyone knows the side effect of too much wormwood in a Draught of Comprehension potion."
"I see." Snape steepled his fingers and considered this information. "You may go, Weasley."
"Um, Professor?"
"Yes, Weasley? Are you still here?"
"Well, that was the second time Malfoy's done that. How long are these side effects supposed to last?"
Snape tilted his head slightly as he looked from the Gryffindor table to his own House's. He did not fail to note the way Granger and his godson were eyeing each other. "I suspect the effects could be rather...long-lived."
Ron paled and left. Snape snorted to himself. Weasleys should never pale. Just makes those despicable freckles more obvious. This got him to thinking about gingers, and then Lily. He sighed almost imperceptibly and went back to his meal.
Later, by the Black Lake:
"I can't believe you did that in front of everyone!"
"Twice." He smugly checked his manicure.
"A potions side effect? Really?" Amusement warred with exasperation in her features.
"What? There can be a side effect when you add too much wormwood, and we both know it!"
"Yes, you blithering idiot - nausea! Thank Merlin no one else in the class knows much about potions."
"So, are you nauseous yet? I've kissed you twice." He showed just the tiniest bit of nervousness. It was utterly endearing.
"Hm...I don't think so. Perhaps more research needs to be done." She pulled him to her by his school tie, and gently placed her lips on his. Things escalated quickly.
Far above them in a window of the castle, a figure in black watched them and smiled to himself. There was hope for the boy yet. 'Long-lived side effects,' indeed.