The oldest boy came striding into sight. He had already changed into his billowing black Hogwarts robes, and Harry noticed a shiny silver badge on his chest with the letter P on it.
"Can't stay long, Mother," he said. "I'm up front, the prefects have got two compartments to themselves."
"Oh, are you a prefect, Percy?" said one of the twins, with an air of great surprise. "You should have said something, we had no idea."
"Hang on, I think I remember him saying something about it," said the other twin. "Once"
"Or twice "
"A minute "
"All summer "
"Oh, shut up," said Percy the Prefect.