Although many people did not remember it, Filch had a birthday too. He often confiscated students' belongings, and the students were unwilling to simply let him take them. They would rack their brains to steal back whatever had been confiscated.
Thus began a tug-of-war: he confiscated, they stole it back; he confiscated it again, and they stole it back again. Severus gave him a quill that could be used against thieves. Whenever someone tried to steal the confiscated items, the quill would jab the thief with its sharp tip.
Filch loved the gift and became utterly loyal to Severus, who had given it to him. Naturally, as someone equally devoted to school order, Filch often reported to Severus what he discovered during his patrols.
Many people still respected the new Defense Against the Dark Arts professor. Everyone knew that what they needed to defend against now was not magical creatures outside the castle, and this genealogist was not particularly skilled at dealing with magical creatures either.
But he upheld the principle of fair competition, treating even Slytherin impartially. Moreover, he could accurately recite the other party's family tree. That won their hearts even more than the Head of House who favored Slytherin and especially targeted Gryffindor.
These families often had family vaults at Gringotts. Carter did not merely communicate with Goblins in the Goblin Office; he also dealt with them. Over time, he learned how to handle people like them.
After giving up on searching the school for Toots's potion formula, Carter turned his attention elsewhere. He began taking an interest in Ben Cooper. If Ben did not want to return to the common room, he could do his homework in Carter's office.
There had originally been nothing strange about that. While Ben did his homework, Carter and Flitwick would