In the late 1990s, Dr. Carla Pugh was working the night shift in the emergency room at Howard University Hospital when a stabbing victim was carted in. He was a John Doe: no wallet, no credit cards, no identification, unconscious. Paramedics had placed a bathmat-size piece of gauze on his chest, and when Pugh peered underneath it, she saw a deep slice in his right chest and a lung hanging out. With such extensive injuries, there should have been a lot more bleeding; but with so little blood loss, the man—despite the savage wounds—should have still been awake. They stripped off all the gauze and bandages when Pugh spotted a tiny hole in his chest. She realized the knife must have nicked his heart. Holy crap, Pugh thought. “Put in a chest tube,” she ordered the resident on her team. “If we don’t get a gush of blood we’ll crack his chest.” When no red geyser was forthcoming, they prepped the patient for emergency surgery, inserting a breathing tube to get him oxygenated and help his heart beat.