It helped that Voldemort wasn't, apparently, entirely dead. It gave him some kind of purpose, even if that purpose was only revenge. But it seemed strange to be casually going about his life, as if at this precise moment the Dark Lord were not plotting to steal the Philosopher's Stone, as if any day he might interrupt everything by breaking into the school. (An odd place to set a trap, Hogwarts; but apparently, Flamel had insisted.) Severus did not care about any of the students as individuals, did not have any particular attachment to any of them as people, but in ten years he had started to really think of himself as a teacher. That meant that he was responsible for them, that the students were under his protection (how strange, that he should expect to be able to protect anyone). He did not like the idea that they were here, in the building, vulnerable to danger should the Death Eaters break into the school, probably - Dumbledore said - with Quirrell's help. This concern, he had not shared; Severus suspected that Minerva would mock him for having acquired a heart.