All the snickering and finger pointing that came in the days following the Defense Against the Dark Arts lesson drove Severus to find counsel in his Death Eater friends who only encouraged him to find a means to seek revenge on Potter and his group of toe rags. His dark eyes had slaved over spell books and texts on Dark Magic while the taunting voices and glances continued mooching his happiness.

"Sectumsempra," he grinned to himself as he wrote it in the margin of his potions book, adding a small memo to only use it on enemies.

Enemies like Potter.