"You sure have!" Tom bounced off his stool and began pacing about. "Now, take porpoises. They utter all sorts of sounds grunts, squeals, jawclaps and one particularly characteristic sound, like the grating of a rusty hinge." Chow scratched his chin uncertainly. "Wal, what about it?" "Suppose I used that rusty-hinge noise to mask the diver's noise." Tom turned and stabbed the air with his finger.