At Slate, shark scientist and blogger David Shiffman breaks down the risks that swimmer Diana Nyad was really taking this week when she swam from Cuba to Florida without a shark cage. The mere phrase “without a shark cage” makes this sound like a huge risk, Shiffman writes. But the historic swim, itself, is the real achievement. The sharks weren’t actually that big of a danger. (BONUS: An explanation of how, exactly, one is supposed to swim long distances inside a shark cage, to begin with.)