"After the fact," said Davis, "I can see how it could happen. But...." He hesitated for a long time and then said, "This is another case where I've been making guesses and hoping I was wrong. And like the others, proof that my early guess was wrong makes another guess necessary. And I dislike the later guess much more than the first." He moved restlessly. "I'm glad you only tried it once, here," he said unhappily. "We're due up at Thrawn Island anyhow. You can work this trick out in the lagoon up there. If there's no reaction to the dredge when we try it, we can try this. But it might be a very violent poke at something we don't quite believe in. I'd rather try a gentle poke first." He turned away. In minutes Nick was belowdecks starting the yacht's engine, two others of the crew-cuts were hauling up the anchor, and the fourth was at the wheel. Without haste, but with celerity, the _Esperance_ headed for the harbor-mouth and the open sea. They had their midday meal heading north by west. Late in the afternoon Deirdre found occasion to talk to Terry about Thrawn Island. "It's the China Sea tracking station for satellites," she told him. "Some of the staff are friends of my father's. It's right on the edge of the Luzon Deep, and the island's actually an underwater mountain that just barely protrudes above the surface. There are some hills, a coral reef and a lagoon. It's also terrifically steep, and you can use the fish-driving device as much as you please without startling any Filipino fishermen." "You've been there before," said Terry. "Oh, yes! I told you a fish wearing a plastic object was caught in the lagoon there. That was when the station was being built. The men at the tracking station fish in the lagoon for fun, and now they're naturally watching out for more ... oddities." The _Esperance_ sailed on. The crew-cuts went about their various chores and talked endlessly, among themselves and with Deirdre, when she joined in. Terry felt useless. He trailed the submarine ear overboard and set the recorder to work as an amplifier only. At low volume it played the sounds of things below. He kept half an ear cocked toward it for the mooing sound he'd picked up at the place where the ocean glittered. He heard it again now, and again found it difficult to imagine any cause for it. The sounds uttered by noisemaking fish are usually produced in their swim-bladders. The purpose of fish cries is as obscure as the reason for some insect stridulations, or the song of many birds. But a long-continued fish noise would involve a swim-bladder of large size. At great depths, if a considerable cavity were filled with gas, under pressures running into tons to the square inch.... Terry could not quite believe it.