"Right, here's what we've got to do," he whispered urgently. "One of us has got to keep an eye on Snape -- wait outside the staff room and follow him if he leaves it. Hermione, you'd better do that.""Why me?"
"It's obvious," said Ron. "You can pretend to be waiting for Professor Flitwick, you know." He put on a high voice, "'Oh Professor Flitwick, I'm so worried, I think I got question fourteen b wrong....'"
"Oh, shut up," said Hermione, but she agreed to go and watch out for Snape.
