Quirrell snapped his fingers. Ropes sprang out of thin air and wrapped themselves tightly around Harry.
"You're too nosy to live, Potter. Scurrying around the school on Halloween like that, for all I knew you'd seen me coming to look at what was guarding the Stone."
"You let the troll in?"
"Certainly. I have a special gift with trolls -- you must have seen what I did to the one in the chamber back there? Unfortunately, while everyone else was running around looking for it, Snape, who already suspected me, went straight to the third floor to head me off -- and not only did my troll fail to beat you to death, that three-headed dog didn't even manage to bite Snape's leg off properly.
‘At’ and ‘for’ are prepositions, and ‘in,’ ‘off,’ ‘off’ are particles of phrasal verbs, aren’t they?
You can look for something or you can look at something. All of the highlighted words are particles of phrasal verbs.