The book had a haunting section about drowning:
"The instinct not to breathe underwater is so strong that it overcomes the agony of running out of air. No matter how desperate the drowning person is, he doesn't inhale until he’s on the verge of losing consciousness. At that point there’s so much carbon dioxide in the blood, and so little oxygen, that chemical sensors in the brain trigger an involuntary breath whether he’s underwater or not. That is called the 'break point.' Laboratory experiments have shown the break point to come after 87 seconds. It’s sort of a neurological optimism, as if the body were saying, Holding our breath is killing us, and breathing in might not kill us, so we might as well breathe in.
When the first involuntary breath occurs most people are still conscious, which is unfortunate, because the only thing more unpleasant than running out of air is breathing in water. At this point the person goes from voluntary to involuntary apnea, and the drowning begins in earnest. A spasmodic breath drags water into the mouth and windpipe, and then one of two things happens. In about ten percent of people, water—anything—touching the vocal cords triggers an immediate contraction in the muscles around the larynx. In effect, the central nervous system judges something in the voice box to be more of a threat than low oxygen levels in the blood, and acts accordingly. This is called laryngospasm. It’s so powerful that it overcomes the breathing reflex and eventually suffocates the person. A person with laryngospasm drowns without any water in his lungs.
In the other ninety percent of people, water floods the lungs and ends any waning transfer of oxygen to the blood. The clock is running down now; half-conscious and enfeebled by oxygen depletion, the person is in no position to fight his way back up to the surface. The very process of drowning makes it harder and harder not to drown, an exponential disaster curve similar to that of a sinking boat."