Caster smiles and accepts the tea, though he does not yet drink. "I can, but the device by which we do so in this time would have to be enormous in order to account for being left unattended. So far, the most efficient means of translating sound to a tangible form uses plastics. Even your longest long-playing records can record an hour at most, with a physical form that is more immediately obvious than that of a hidden camera. If there were a way to turn sound into something that could be read with something smaller than a gramophone--which I'd have to come up with too, come to think of it. Perhaps light. If there were a device that could read light and convey it as sound..."

His Master's displeasure is obvious. And valuable, for that matter, though not lightly taken.

"As I said," Caster concludes, "it is much more difficult to capture sound than frames of motion. And I think that, by the time I developed this technology, the war would be at our doors."