While documenting leopard seals in Antarctica for a 2006 National Geographic magazine story, photographer Paul Nicklen had an experience that he says "will stay with me forever" (see Nicklen's photos). That experience has recently resurfaced and gone viral on the Internet, thanks to remixing and postings on Facebook and other outlets.

"Leopard seals are the most incredible animals I've ever had the pleasure of photographing," he said. "When you get in the water with a wild animal, you're essentially giving yourself to that animal because, as humans, we're quite helpless and vulnerable in the water. You're at the seal's mercy. You're at the predator's mercy.

"Not only did the leopard seals not attack as some predicted they would, they fed me penguins, followed me around, and generally put on a nonstop show."

In the video above, Nicklen explained how an encounter with one particular female leopard seal was especially poignant. The animal had a head larger than a grizzly bear's, and it took his camera and his head into its mouth.

But instead of harming him, the seal began to "nurture" him. It began to bring him penguins, first alive, then dead, perhaps assuming that he was a "useless predator in her ocean."

The top predator apparently tried to feed the weaker Nicklen for four days as he scuba dived in the area, working on the assignment.

(See more behind-the-scenes videos of Paul Nicklen photographing polar bears and walruses.)