The effect was startling.

The men uttered a yell of fright, and started in a panic run for the boats, but the leader threatened them with his leveled pistol and stopped them, although the frightful groan came a second time.
"There's nothing in the bush!" Robert heard him say.

"There can't be! The place has no people and we know there are no big wild animals on the islands in these seas! It's some freak of the wind playing tricks with us!" He held his men, though they were still frightened, and to encourage them and to prove that no enemy, natural or supernatural, was near, he plunged suddenly into the bushes to see the origin of the terrifying sounds.

His action was wholly unexpected, and chance brought him to the very point where Robert was.

The lad leaped to his feet and the pirate sprang back aghast, thinking perhaps that he had come face to face with a ghost.