Suddenly a roar burst out of the air just above their heads. The two leaped to their feet.
"It's Chuck!" Cooper yelled. "He's back!"
The helicopter made a half-turn of the camp and came rapidly to Earth.
Trumpeting with terror, Old Buster was a dwindling dot far down the grassy ridge.
III
They built the nightly fires circling the camp to keep out the animals.
"It'll be the death of me yet," said Adams wearily, "cutting all this wood."
"We have to get to work on that stockade," Cooper said. "We've fooled around too long. Some night, fire or no fire, a herd of mastodon will come busting in here and if they ever hit the helicopter, we'll be dead ducks. It wouldn't take more than just five seconds to turn us into Robinson Crusoes of the Pleistocene."
"Well, now that this recognition thing has petered out on us," said Adams, "maybe we can get down to business."