The encounter happened on a Wednesday morning, in the corridor between the Potions classroom and the staircase that ran from the dungeons to the second floor.
He had been walking from the library — the east window table, the early session before breakfast, the specific productive quality of an hour spent before the castle had fully assembled itself for the day. He had his bag over one shoulder and his dark-covered notebook in his hand, which was where it usually was when he was moving between places and wanted to keep the thinking going rather than lose it to the transition. He was working on the ward perimeter question that Dumbledore had set him at the end of the previous Tuesday session — the specific problem of how a fixed ward reacted to a mobile practitioner maintaining an internal field, the interaction between two working types that most ward theory treated as incompatible categories.
He was thinking about the incompatibility when Snape came around the corner.
The encounter had the specific quality of two people turning into the same corridor from opposite ends with enough time to see each other coming and not enough time for either to have decided what to do about it. The corridor was not empty — a pair of first-years were moving in the same direction toward the stairs, oblivious in the way first-years were oblivious at seven forty in the morning — but it was quiet enough that the space between them was its own particular thing.
Snape looked at him.
He had been looked at by Snape for three years now and had learned the specific gradations of it. There was the looking that was inventory — the beginning-of-class sweep, assessing who was there and whether their workstations were set up correctly. There was the looking reserved for perceived insolence, which had a quality of focused preparation, like a wand being drawn. There was the looking he gave Neville, which was the looking of someone who had decided that a person was going to fail and was watching the failure occur with the patience of someone confirming a conclusion they had already reached.
The looking he gave Ron now was none of those things.
It was the looking of a Legilimens.
Not aggressive — not the specific penetrative quality of someone forcing entry. More the quality of someone who, encountering another person, performed a habitual check the way a practitioner checked the temperature of a room or assessed the ambient field. An intake of information at a level just below consciousness. The kind of look that most people never recognized because most people had nothing constructed behind their eyes that would register it as an attempt.
He met it with the flat settled quality of closed rooms. Not aggressive in return — not a defense that announced itself as a defense, which would have been its own kind of information. Simply: not available. The doors were closed, the windows shuttered, the structure present and complete and giving nothing away.
Snape stopped.
It was a brief stop — two steps from his previous pace becoming one, not a full halt, not something observable to the first-years who had already reached the stairs. But it was a stop, and it was produced by something he had encountered that he had not expected to encounter.
He looked at Ron for another moment. The quality of the look had changed entirely. The inventory was gone. The confirmation-of-conclusions was gone. What was there was the specific expression of a practitioner who had performed a routine assessment and received a non-routine result and was revising his operating assumptions in real time.
Ron held his gaze. He offered nothing. He did not perform surprise or discomfort or the apologetic quality that the corridor encounter seemed to be inviting from him, because performing those things would have been offering information, and offering information to Snape was not a thing he did on principle.
'Mr. Weasley,' Snape said. His voice had the quality it had when he was delivering a statement that was ostensibly neutral and contained a question that he had decided not to ask directly, because asking it directly would have required acknowledging that he didn't already know the answer.
'Professor,' Ron said, in the tone of someone acknowledging a corridor encounter, which was all it was.
Snape's eyes moved, briefly, to the dark-covered notebook in Ron's hand. Then back to his face. The assessment continued for a moment — the specific quality of someone who had a great deal of practice at building accurate pictures from limited information and was doing it now with the concentrated attention that the situation appeared to warrant.
Then he walked past.
Ron let him go. He did not look back. He walked to the staircase and took the second step and continued toward the library with the steady quality of someone who had had a conversation that confirmed a thing he had already suspected and had filed it correctly.
Snape now knew that Ron Weasley could close his mind.
He had not known this before. He had assumed — as most people assumed, as most people were correct to assume — that a fifteen-year-old Gryffindor in the middle years of his Hogwarts education had a mind that was as open as any other fifteen-year-old's. The assumption was reasonable. The assumption was wrong.
Ron had been waiting for the moment Snape would notice. He had been waiting with the patient quality of someone who understood that the noticing was inevitable and had prepared for its arrival rather than attempting to prevent it. Snape was not a person who could be prevented from noticing things indefinitely. He was observant in the specific way of someone for whom observation was not a hobby but a survival skill, and the quality of his attention to the world around him was one of the things that had kept him alive for decades in conditions that had not been conducive to longevity.
The noticing had arrived. It had arrived cleanly, without confrontation, without any information being exchanged that Ron had not intended to exchange.
He went back to the ward perimeter problem in his notebook and found, as he rounded the corner toward the east staircase, that the incompatibility question had resolved itself in the corridor, the way these things sometimes did when the mind had been working on a problem slightly below the level of conscious attention and had produced the answer in the margin of something else.
He wrote it down before the staircase could take it.
He was at the library window table by five past eight, and the tea that Sable had arranged was still warm, and the morning was proceeding as mornings did when the things that needed to happen had happened correctly.
He did not think about Snape again until Potions on Thursday, when Snape arrived at his workstation during the reduction stage of the Strengthening Solution, looked at his cauldron with the specific quality of someone performing a genuine assessment rather than looking for something to critique, said nothing, and moved on.
The nothing was different from his previous nothings. He filed the distinction without expression and returned to the reduction stage, which had reached exactly the correct rate of bubble formation and required his full attention to keep there.