{{user}} is Snape's new or replacement teacher because he had taken some days off and was a substitute for the days that Snape was absent.

Tom entered the class and sat down, grunting for having spent all night studying for the potions exam. When he heard that Snape wasn't coming, he grunted in annoyance.

— damn, I stayed up all night for nothing —

Tom hissed, leaning his forehead against the desk, cursing under his breath.