The following is part of a top ten list written originally for The Times (London) by Richard Coniff from his new book Swimming with Piranhas at Feeding Time: My Life Doing Dumb Stuff with Animals (W.W. Norton). One morning in my mid-life crisis, when I had considered and rejected the thrill-seeking possibilities of nude skydiving or drag-racing on a mountain road in a red Corvette convertible, it occurred to me that it might be a good idea to go for a swim in a tankful of hungry piranhas at feeding time. Soon after I was standing in the dark in front of the piranha tank at the Dallas Aquarium, surrounded by seven-year-olds excitedly telling one another how quickly piranhas can reduce a human being to bloody stew. One of the boys was lashing his head from side-to-side, teeth bared. Then a couple of others joined in, swarming around me. The aquarium's piranhas were bigger than I expected, some nearly a foot in length, and there were 40 of them in an area not much larger than a hot...