Miguel made no further mention of his challenge and David was careful not to remind him of it. It was not until several weeks later that the matter again came up, with consequences as unexpected as they were startling. For the present David was fully occupied with the venture in hand. There were a hundred things he wanted to learn and the questions he asked were many. The men, however, were reluctant to talk on most subjects and he finally came to the conclusion that their reticence was the result either of ignorance or of orders from higher up. They were glad enough to help him with his study of their language--so far as they themselves knew it; to tell him about the river or the animals; and of the methods employed in collecting and preparing the rubber latex. But when he asked about Rice, the ranch, or kindred things they remained ominously silent. After a while David did not mention these subjects again. It was too evident that the men did not want to discuss them. A week later they entered a river that joined the Solimoes from the west. It was a small stream compared with the one into which it emptied--not over a few hundred yards in width. At least, the channel they had entered was narrow and the water was clear and swift so that the launch made slow progress. When David looked down at the water speeding past them it seemed that they must be moving along at a furious rate; when he looked at the trees on the bank he knew that they were barely making any headway. It took several hours for them to battle their way up the turbulent stretch of rapids. “That is an island,” said one of the men, pointing to the land on their right. “This channel is bad enough--especially when the water is low. But you should see the branch on the other side of the island. There is a drop there several meters high and no boat can pass up or down it.” David was not greatly impressed by these words. He did not recall them even later when he found himself suddenly at the brink of that very drop. The country rapidly became wilder in appearance. Perhaps it only seemed so because the stream was so narrow that they had a continuous close view of both banks and the heavy growth that clothed them. The launch seemed strangely out of place in the dreary, primeval waste of jungle and hurrying water. Men had come and gone before on the river; and Indians and beasts lived in the green fortresses on either side. But there was no sign of them, no trace of their presence or existence. Only once was there evidence that others besides themselves were stirring on the now silent, undemonstrative river.