45 minutes after diving under the ice into the frigid water of the Arctic, Paul Nicklen's body starts uncontrollably shivering.
He can't feel his fingers — or the camera in his hands — at all. The only way he knows he's actually taking pictures is to watch his finger hit the shutter button on the camera.
But he keeps pressing on, taking photos, until the early stages of hypothermia start to set in and everything starts to slow down. That's when he knows it's probably time to wrap up the shoot.