" I give you a riddle,’ Olsen said suddenly. ‘It is black. It has eight wheels. But it is no vehicle. What is it?’ His penetrating, slightly protuberant eyes surveyed them as they shook their heads. ‘What is it?’ he repeated. ‘We shall not find that,’ Josef said. Olsen gave a short laugh. ‘A priest, on roller skates. I give you another riddle. It is greater than the universe. It is less than a grain of sand. The dead eat it. If we eat it, we too shall be dead. "

― John Christopher , The White Voyage