From Soul Music by Terry Pratchett
She'd seen other things. For example, she'd never mentioned the strange woman in the dormitory the night Rebecca Snell put a tooth under the pillow. Susan had watched her come in through the open window and stand by the bed. She looked a bit like a milkmaid and not at all frightening, even though she had walked through the furniture. Theere had been the jingle of coins. Next morning the tooth had gone and Rebecca was richer by one 50-pence coin.