Water had some powerful, unknown capacity to slow humans’ hearts, and the blood in their bodies began flooding away from their limbs and toward their vital organs. He’d seen the same thing happen in deep-diving seals decades earlier; by shunting blood away from less important areas of the body, the seals were able to keep organs like the brain and heart oxygenated longer, extending the amount of time they could stay submerged. Immersion in water triggered the same mechanism in humans.