This same day others of our party had an interesting experience with the creatures in another pond.  One of them was Commander da Cunha (of the Brazilian Navy), a capital sportsman and delightful companion.  They found a deepish pond a hundred yards or so long and thirty or forty across.  It was tenanted by the small caymans and by capybaras—­ the largest known rodent, a huge aquatic guinea-pig, the size of a small sheep.  It also swarmed with piranhas, the ravenous fish of which I have so often spoken.  Undoubtedly the caymans were subsisting largely on these piranhas.  But the tables were readily turned if any caymans were injured.  When a capybara was shot and sank in the water, the piranhas at once attacked it, and had eaten half the carcass ten minutes later.  But much more extraordinary was the fact that when a cayman about five feet long was wounded the piranhas attacked and tore it, and actually drove it out on the bank to face its human foes.  The fish first attacked the wound; then, as the blood maddened them, they attacked all the soft parts, their terrible teeth cutting out chunks of tough hide and flesh.  Evidently they did not molest either cayman or capybara while it was unwounded; but blood excited them to frenzy.  Their habits are in some ways inexplicable.  We saw men frequently bathing unmolested; but there are places where this is never safe, and in any place if a school of the fish appear swimmers are in danger; and a wounded man or beast is in deadly peril if piranhas are in the neighborhood.  Ordinarily it appears that an unwounded man is attacked only by accident.  Such accidents are rare; but they happen with sufficient frequency to justify much caution in entering water where piranhas abound.

We frequently came across ponds tenanted by numbers of capybaras.  The huge, pig-like rodents are said to be shy elsewhere.  Here they were tame.  The water was their home and refuge.  They usually went ashore to feed on the grass, and made well-beaten trails in the marsh immediately around the water; but they must have travelled these at night, for we never saw them more than a few feet away from the water in the daytime.  Even at midday we often came on them standing beside a bayou or pond.  The dogs would rush wildly at such a standing beast, which would wait until they were only a few yards off and then dash into and under the water.  The dogs would also run full tilt into the water, and it was then really funny to see their surprise and disappointment at the sudden and complete disappearance of their quarry.  Often a capybara would stand or sit on its haunches in the water, with only its blunt, short-eared head above the surface, quite heedless of our presence.  But if alarmed it would dive, for capybaras swim with equal facility on or below the surface; and if they wish to hide they rise gently among the rushes or water-lily leaves with only their nostrils exposed.  In these waters the capybaras and small caymans paid