None of the humans could hear the noise that was broadcast from the box, but the eagles turned and flapped away swiftly to escape the eardrum-paining frequencies.
Immediately after, Barney said, "Doc! Wolves ! "
Doc looked up and saw the first of the big beasts bounding over a bush to their left. But it was not a wolf. It was a large blackish German shepherd dog. Behind him came three more and behind them six big Doberman pinschers. Their mouths were open, revealing their sharp teeth, but they uttered no sounds.
A few minutes later, they turned and bounded away as if they had seen a pack of tigers.
Doc and his party climbed on toward the excavation, taking advantage of every bit of cover. The eagles and the dogs would undoubtedly be back. The noise had momentarily overcome the stimulus of the microcurrent in the hostility area of their brain. But once they were out of the influence of the supersonic frequencies, they would return.
"How can they see us, Doc?" Pauncho said. "I mean, how can the operators of the control boxes see much through the eyes of the animals in this dark?"
"I doubt they're using TV tonight," he said. "It's too hard to keep the narrow beams locked in under these conditions. They probably are just transmitting the code that turns on the juice to the aggression areas of the brain and letting the animals attack whatever they come across.
"I hope so, Doc," Pauncho said. "If they can spot us through the eyes of the birds, we're going to have a hard time.
"Here they come again," Caliban said. He had turned the sound generator off so that the animals would not be affected until they got close.
The eagles, their only noise the flapping of their wings, and the dogs, their only noise the brushing aside of the wet rain-covered plants, came in swiftly. They had but one intention: to tear apart these strangers in the dark.
Then Doc pressed the button, and the dogs whirled so fast they slipped in the mud and fell on their sides or scrabbled desperately to keep from sliding on down the slope. The eagles veered away and were swallowed by the night.
A minute later, the birds and the dogs were charging in again.
Thirty seconds later, they were frenziedly trying to get away from the invisible agony.
"How long's this going on, Doc?"
"Until something—or somebody—breaks," Caliban said.
Pauncho knew it was useless to ask him to elaborate.
The next time, the birds came in first and the dogs did not appear until the birds had been turned away.
"They're catching on," Barney muttered.
"And probably moving in on us," Pauncho said.
"Isn't it really too risky to stay in this one spot?" Cobbs said. "I think we should be moving about a bit."
"That's up to you," Doc said. He pressed the button again as the first of the birds appeared. This time they kept on coming and had almost reached them, with Doc saying, "Hold your fire! " when they broke and flew upward.
The dogs bounded down the slope again, just as the birds turned away. Doc said, "Hold your fire on these, too, unless you can stick your guns down their throats."
"The whites of their eyes, heh, only closer yet?" Pauncho said.
Some of the dogs slipped in the mud and slid into them. The others turned away just before the final leaps and went crashing into or over the bushes and down the hill.
Three dogs hurtled in, sidewise or fangs first, and Pauncho and Barney slammed one each over the head or the back and then kicked them on down the hill. Cobbs and Villiers hit a dog at the same time with the barrel of their rifles, breaking its ribs.
Doc said, "It ought to be over soon, one way or the other."
"What makes them voiceless?" Pauncho said. "I looked in the neck of a bird with its throat cut open back at the house on the mountain, and its vocal cords were all there."
"I saw you," Doc said. "But I supposed you'd guessed the answer. There are a number of electrodes at various areas of the brain. During the time that the animal is released for attack, its voice centers are inhibited."
"I wondered about that," Cobbs said. "But things have been happening so fast, I didn't have time to ask about it.
"I just supposed their vocal cords had been cut," Barbara said.
The others did not comment. Pauncho had asked Doc about the lack of voice after the attack by the wolves in the castle and Doc had given his opinion. But after the attack of the birds at the house on the mountain, he had told his colleagues not to mention anything about the characteristics of the animals. He had wanted to determine if the English couple would be curious about the strange lack of cries from the animals. If they did not comment, they might refrain because they knew the reason.
On the other hand, it was true that events had come one after the other and might have distracted them. But Barbara seemed to be a very stable and self-possessed person, and Cobbs, though he showed some apprehension, was far from hysterical.
The birds came first and the surviving dogs, going much slower because they had to climb uphill in muddy earth, attacked simultaneously. This time the wings of the eagles beat so close that the tips of some touched their faces. But the birds swerved again and shot back overhead. The dogs turned tail when they were still a few feet from closing with the party.
"I'd think they'd go crazy," Barney said. "They're being pulled apart by the opposing drives."
"They may yet," Doc answered.
About two minutes later the birds came in again, and this time Caliban turned off the sound generator for a few seconds after they had wheeled around to go in the other direction. The dogs then had nothing to stop them except the weapons of the party. While the others knocked the dogs on the head as they struggled uphill to get at them, Doc Caliban pressed a button on the other box, which had been on the ground by him. He had rearranged its circuits so that the aggressive areas of the brains would be stimulated.
The others did not notice what he was doing, since they were concentrating on smashing in the dogs' skulls or backbones and doing a good job of it. He had not told them his plan, since he never confided to anyone unless he needed cooperation.
There were yells and screams to the right up the mountain, and then rifles and pistols banged away. Doc indulged himself with a broad smile. The others had their backs turned and would not be able to see him.
He switched off the aggression transmitter and turned on the sound generator. The two surviving dogs leaped backward down the hill as if, they had stepped on a red-hot plate. One turned over and kept on sliding. The other regained his feet and fled.
"What's going on, Doc?" Pauncho said, jerking a thumb in the direction of the gunfire.
"As soon as the birds were deflected again, and presumably heading back toward the men who'd launched them, I switched off the noise generator and turned the aggression stimulation on. The birds, of course, attacked the first living things they saw, which were our enemies."
"Fabulous!" Pauncho rumbled. "I wish I had one of those hemispheres stuck on Barney's head. Then I could keep him from making a monkey of himself."
"Since when does a monkey's uncle know anything about proper behavior?" Barney said.
"The conflict of noise generator versus aggression stimulation might have driven them mad, anyway," Doc said. He led the way toward the groanings and whimperings drifting ghostily through the bushes. Approaching cautiously, they found six men on the ground, all alive but three totally unconscious and the other semiconscious. The birds were all dead, since they had not ceased to attack until killed. The onslaught had been so unexpected that none of the men had had time, or opportunity, to turn off the aggression stimulator. The birds had tried for the face and the throat and had blinded four. One man died of a ripped jugular vein while Doc was examining him.