Professor Trelawney teaches Divination, the art of telling the future. She's also an old fraud. She always predicts death and bad luck for Harry: it's her favorite trick. When Ron and Harry make up a month-long series of predictions of horror and misfortune for themselves, Professor Trelawney praises them enthusiastically. She does seem to have some real talent hidden away somewhere, though. At the end of Book 3, she predicts the rise of Voldemort once more. But Professor Trelawney seems utterly unable to make her future-telling talent work on command.