Severus Snape didn't deem himself to be an insomniac and by no means he was one who loved sleep, but he had a long list of Constructive things he could find himself doing in the middle of the night. He found himself losing a bit of hours of sleep in exchange for some special potion or a tad bit of advance in one of his researches. He was used to late hours, to pot of teas in the solitary staff room, he was used to his solitude.
So he didn't expect anyone when he entered the room in a swift of black, long, worn-out robes, and when he saw there was someone there and his pot had been occupied already, he scowled disappointed. "Professor Burbage." he greated stiffly, his dark eyes scanning the person in front of him for a moment. And then there it was, that awkward silence he knew not how to fill as he thought about what to do. Leaving maybe, or just share the pot for ten long silent minutes before coming back to his solitude, he tried to weight the options.