How does Tom shock aunt Polly into giving him a special apple she had been saving for him?

When Aunt Polly gets angry at Tom for not letting her know he's not dead. So he recounts his secret visit as a dream. At the end of his tale he says that in his dream he wrote on apiece of sycamore bark that they weren't dead, then kissed her. Aunt Polly believes that "A body does just the same thing in a dream as he'd do if he was awake." and then she gave him an Apple.