i just feel very lucky to be alive right now. >> elbow reef, key largo, florida. cozy with a diver and sends him to the hospital. >> instantaneously it hurt. it was almost like a firecracker going off in my mouth. >> for more than a decade, diver dave marcel has been leading scuba tours for curious thrill seekers. >> working with wild animals in their natural habitat is something that most people only could dream of. >> the reef is teeming with life. fish of all shapes and sizes, beautiful coral, a rare chance to interact with some of the planet's most interesting characters. >> we had numerous animals. we had nurse sharks, barracudas and goliath groupers and green moray eels. these are my pets. most people have cats and dogs. i have animals under water. >> the sea pro gives his clients a little something extra, physical encounters with sea creatures that strike fear into the saltiest seafarer, like the 300-pound nurse shark. dave feels the key to the carnivores' trust is physical affection. >> whenever you hold a nurse shark, they typically just go to sleep. they