Severus felt a glimmer of amusement at Regulus' astute observations. At least he knew that if this was some sort of game, it wasn't one being served up by anyone other than a Slytherin. Anyone else would no doubt have had Regulus feel hurt by Severus' suspicions.
He narrowed his eyes as he followed Regulus, half his attention on what he was saying and half on the castle. He had a lot of knowledge that Regulus couldn't have known, unless what he was saying was true. Or this was an elaborate game. Though if it was the latter, the timing was terrible.
He was just rolling his eyes at the mention of some of the people who were apparently here and was about to say something pithy when he set foot in the Entrance Hall. It was at that moment that the castle just grabbed at him... or rather grabbed at all the connections that the Headmaster had with it. He grunted and locked his knees as the castle flooded him with information and, for lack of a better term, emotions. The level of sentience of the castle had often been a subject of debate among the portraits in the Headmaster's office without any firm conclusions being made. Severus was right now of the opinion that the castle was possibly more sentient than most realised.
It was also... lonely. And backing up everything Regulus was saying. He pinched the bridge of his nose for a moment, then ran his hand down his face.
"That was entertaining," he said dryly as the castle receded enough to let him think, though it still clung to him tightly, like a frightened child. It was a disconcerting feeling. "The castle is backing up your story."