Through the Brazilian Wilderness by Theodore Roosevelt

The morning after our arrival at Corumbá I asked Colonel Rondon to inspect our outfit; for his experience of what is necessary in tropical travelling has been gained through a quarter of a century of arduous exploration in the wilderness. It was Fiala who had assembled our food-tents, cooking-utensils, and supplies of all kinds, and he and Sigg, during their stay in Corumbá, had been putting everything in shape for our start. Colonel Rondon at the end of his inspection said he had nothing whatever to suggest; that it was extraordinary that Fiala, without personal knowledge of the tropics, could have gathered the things most necessary, with the minimum of bulk and maximum of usefulness.

Miller had made a special study of the piranhas, which swarmed at one of the camps he and Cherrie had made in the Chaco. So numerous were they that the members of the party had to be exceedingly careful in dipping up water. Miller did not find that they were cannibals toward their own kind; they were "cannibals" only in the sense of eating the flesh of men. When dead piranhas, and even when mortally injured piranhas, with the blood flowing, were thrown among the ravenous living, they were left unmolested. Moreover, it was Miller's experience, the direct contrary of which we had been told, that splashing and a commotion in the water attracted the piranhas, whereas they rarely attacked anything that was motionless unless it was bloody. Dead birds and mammals, thrown whole and unskinned into the water were permitted to float off unmolested, whereas the skinned carcass of a good-sized monkey was at once seized, pulled under the water, and completely devoured by the blood-crazy fish. A man who had dropped something of value waded in after it to above the knees, but went very slowly and quietly, avoiding every possibility of disturbance, and not venturing to put his hands into the water. But nobody could bathe, and even the slightest disturbance in the water, such as that made by scrubbing the hands vigorously with soap, immediately attracted the attention of the savage little creatures, who darted to the place, evidently hoping to find some animal in difficulties. Once, while Miller and some Indians were attempting to launch a boat, and were making a great commotion in the water, a piranha attacked a naked Indian who belonged to the party and mutilated him as he struggled and splashed, waist-deep in the stream. Men not making a splashing and struggling are rarely attacked; but if one is attacked by any chance, the blood in the water maddens the piranhas, and they assail the man with frightful ferocity.