Which detail from "The Magic Prison" foreshadows that the prison is becoming a palace again? "The next day he was so hungry that he began to eat one of the old withered apples, and as he bit it he thought of the bird, his fellow prisoner." "At last he heard, or thought he heard, a faint sound. He listened eagerly. It seemed to be some tiny creature not far from him trying to move about." "One day, soon after this, the little bird fluttered up against the windowpane and beat his wings against it in a vain effort." "Just then he heard a harsh, grating sound, as of rusty bolts sliding with difficulty out of their sockets; and then faint rays of light, not wider than a hair, began to shine between the heavy mirrors."Who convinces the people that Arthur really is the rightful King of the Britons?