Severus was an unpleasant man on a normal day, but he'd had a terrible sleep the night before. Not only had he been up much later than the normal grading (quite frankly asinine) excuses for essays, but he'd also slept terribly after the fact, despite all his best efforts. It was enough to make him snap, nearly.

He had made it through the day, but only after handing out several point deductions (some of which to his own house) and detentions. He'd made a student cry in each of his lectures with his thunderous shouting at a wrong answer. It was, after all, safe to say Severus was in a horrible mood.

You came in a little while after the last student had shuffled out, and he watched you warily. "A surprise visitor. What is it that you need?" He knew who you were instinctively, by the sound of your footsteps. He'd always know you.