That’s how Ptolemy imagined the disposition of his memories, his thoughts: they were still his, still in the range of his thinking, but they were, many and most of them, locked on the other side a closed door that he’s lost the key for. So his memory became like secrets held away from his own mind. But these secrets were noisy things; they babbled and muttered behind the door, and so if he listened closely he might catch a snatch of something he once knew well.