Morsmordre

Snape gripped the wand in his hand, clutching it so hard the wood left imprints in the clammy, rough skin of his palm. He silently shivered as he felt the constricting bond of the unbreakable vow loosen and cast itself from him. It was over, finally, this thing, this abomination that had been asked of him, begged of him, once in friendship and once in fear. He heard the commotion around him, the mad cackling of Lestrange, the raucous cheers of the other Death Eaters, and the screech of a wicked spell being cast. He turned to see Bellatrix, her arm outstretched, a malevolent look of triumph upon her face; it sickened him. He cast his eyes towards the night sky, filled with thousands of stars, and watched as the Dark Mark blossomed above the castle like a poisonous flower, blooming in celebration of a sick and twisted victory...

(Canon? Not really.)

(The image of Morsmordre is taken from a film still. I did not draw it.)