Having just eradicated a rather stubborn boggart that had lodged itself in his office desk, and subsequently having reminisced about the time when Lupin, as Defence Against the Dark Arts Teacher, had humiliated him school-wide with Neville's boggart, it was safe to say that Professor Snape was in a rather vindictive mood.

Which was unfortunate for those whose essays he was currently marking, on the subject of Moonstone and It's Uses in Potion-making. It was the usual garbage- incoherent thoughts strewn messily on to paper at the last minute. After some time, his hand began marking "T"s on the papers almost sub-consciously, as his concentration drifted elsewhere and he began to fall asleep.

Having spent the last hour putting out fires in all of the common rooms, Dobby started roaming the halls of the school, trying to find somthing, anything to do after hours.
As he passed a particular door, he heard sounds of light snoring. Being the curious house elf that he was, he decided to see who it was that was snoring. As he snuck in quietly, he noticed a mop of black hair on a desk. Soon, he found himself walking towards this mass of hair, and when he reached it, he began inspecting it by tugging on a few strands.

He was near a bubbling cauldron... Neville Longbottom was inside it... The boy grabbed Snape by the hair, pulling him downwards, into the potion...

He awoke with a surprised jump. Two enormous green eyes were staring at him, curious and almost apologetic.

"What-"he stammered, confused.Then- "Who on earth let you in here?" he hissed, coming to his senses, recognizing the intruder as a house-elf.

Dobby immediatly released the hair, and jumped back. He looked up into the eyes of the potions master.

"D-dobby is sorry, sir. Dobby should not have pulled on Proffesor Snape's h-hair."
He took a few steps back, and turned so that he was facing the wall.

"Dobby will punish himself, sir."
Suddenly, the Snape's office was filled with the sound of a house elf slamming himself against the stone wall.

Perhaps it was the heat -the fire place had been warming his cramped office for far too long- but he felt a slight amount of pity for the creature now slamming itself, shrieking as it did so, against the walls.

Still, he snapped. "Stop that, will you?"

Dobby did not stop. His cries seemed to grow louder. Snape's head throbbed in pain, his irritation growing until he could not bear it anymore. Reaching out, he smacked the house-elf rather more violently than he had meant to, and in a rather different spot than he had meant to- on the elf's buttocks.

Dobby stopped. He felt this electric shock flow through his entire body from where the potions master had just hit him. "S-sir, Dobby is feeling strange, Dobby feels like he got socks!"