When Filch wasn't guarding the scene of the crime, he was skulking red-eyed through the corridors, lunging out at unsuspecting students and trying to put them in detention for things like "breathing loudly" and "looking happy.

“He hardly heard what Professor McGonagall was telling them about Animagi (wizar…”

“Great, tell me when you've defeated Voldemort for me, will you?”

“And as she jogged out of sight, they could hear her muttering, "Tentacula. Devi…”

“Hermione launched herself forwards and started punching every inch of him that …”