"Professor Snape! What are you doing, crouched there in the snow?" Poppy was surprised - she had almost fallen over him. She pinched her lips together. He had clearly been out some time, and without a proper coat. He was shivering.
He started as well, as her shadow passed over him and the area on which he was concentrating so intently. "I needed some snow-lichen for the Florid Fever potion, before the Hospital Wing overflows with wretched wailing children. I've walked half a mile, and look! Here it is attached to the edge of this stone staircase." His voice was apologetic, as it only became for her.
The lichen fairly glowed, brilliant fiery orange-red against the white snow.
She watched as he carefully scraped it off into one of his vials.
"Now, please join me in the warmth of my office. I will make you some hot chocolate. No, I insist. It is medicinal." But she smiled fondly.
"Thank you, my dear." He rose and gestured, ushering her politely up the stairs before him, again admiring the clean crispness of her nurse's cap. "I know how to take my medicine."