Despite the way they ate Charlton Heston's horse from under him in the movie, piranhas are said not to attack anything that is not injured and bleeding. Some members of our party cool off routinely by swimming in the river and not one of them is skeletonized. On the other hand, if you take a bloody piece of water buffalo meat and lower it into the same water on a hook and line, you feel a vibration like electric current as swarming piranhas saw away at the tough meat. If the biting slows down, the canny piranha angler whips the water surface with his Amazon equivalent of a willow pole and the piranhas get excited and renew their attack on the buffalo meat. We adults can't fish effectively without our neoprene waders and our graphite fly rods, but some kids who came with their parents are less spoiled and they catch several and have them for dinner.
Man bites piranha.
The most powerful impression I have of the Amazon rain forest is the overwhelming numbers of species. Compare that to your Montana lodgepole forest. For some reason, plants in the Amazon usually don't grow near other plants of the same species. Nobody knows why, though theories abound. Nobody knows how many species of katydids live here, for example, but our bug walks demonstrate that there are worlds, maybe whole galaxies of katydids.