There was little need for caution. On climbing up the rocky ledge they found the anaconda still engaged in swallowing its prodigious meal. The reptile was about twenty-five feet in length and normally as big round as a man's thigh, but now it was tremendously distended in spite of the fact that the head and half of the body of the jaguar, crushed almost to a pulp, had yet to be consumed. It was not a sight to watch for long. The men returned to the boat. Then Uncle Brian unburdened himself. "Don Ramon and his pals evidently don't want us to return to El Toro," he said abruptly. "I'm not altogether surprised at that," rejoined Peter. "But where are your proofs, Uncle?" "Here," replied Brian, indicating his double-barrelled gun and the petrol tins. "This gun has been tampered with. The striking mechanism has been thrown out of action. That's why you had two missfires. And the petrol has been liberally watered; I guessed as much when it spluttered. Before we get under way, we must pass every drop of petrol through a strainer." The gun was beyond repair with the limited tools at their disposal. For all useful purposes the weapon and a hundred shot-cartridges were so much lumber. They had better luck with the "doctored" petrol. By means of a strainer and a piece of fine muslin, the spirit was practically freed from water. In the process the fuel supply was appreciably diminished, for every tin had been tampered with, except the one which had supplied the petrol for the previous day's run. The double discovery was a disconcerting one. Nevertheless, it left Brian Strong a tolerably free hand. The mask was off. Either Don Ramon Diaz had his suspicions, or else he had no longer any need for the Englishman's services, and in that case had no scruples about descending to a trick by which Brian and Peter might meet with disaster and death in the wilds of the Upper Rio Guaya, or its tributary the Rio Tinto. It was half-past eight in the morning before the voyage was resumed. Before long, the confluence of the Rio Tinto and the Rio del Morte was sighted. Brian, who was steering, ported helm and shaped a course towards the left bank, where the latter tributary joined its coffee-coloured waters with those of the Rio Guaya. Presently Peter, who was engaged in cleaning out the barrel of his Express rifle, happened to glance skywards. Following the boat at a height of about two thousand feet was one of the units of the Rioguayan air fleet. How long the flying-boat had had them under observation, neither Peter nor his uncle could say. The rapid throb of the outboard motor had prevented them hearing the deeper roar of the flying-boat's quadruple engines.