"Reminiscing," Harry said at once, with a choked laugh, "He’s so confident that he’s at not at risk, that he’s having a look around. He thought of Hogwarts as his home, you know... he missed it," when the dot that was Voldemort wandered into the great hall, Harry jumped into action, "Right - we need to go. Now," he said firmly, "Dobby," the elf squeaked, "I need you to alert Professor Snape now, okay?"