Percy: Gryffindors, keep up please. And stay alert! Harry: How could a troll get in? Ron: Not by itself. Trolls are really stupid. Probably people playing jokes. What? Harry: Hermione! She doesn't know! Ron bit his lip. ‘Oh, all right,’ he snapped. ‘But Percy’d better not see us.’ Ducking down, they joined the Hufflepuffs going the other way, slipped down a deserted side corridor and hurried off towards the girls’ toilets.