In this episode, Doc Gruber and a colleague are testing a shark repellent. If effective, it could help save the lives of divers, swimmers and surfers all over the world.

Here's some more stunning underwater footage. This time it's hammerhead sharks and stingrays, a wahoo and some striped eels, all filmed near the Cocos Island in the Caribbean. Take a look!

Samuel Gruber's team films white-tipped sharks and barracuda feeding at night off Cocos Island. Enjoy!

The great white shark and killer whale are both infamous marine predators. Normally they leave each other alone, but one day, biologists off the cost of California witness something unprecedented.

Several boats converge near the largest of the Farallon Islands when killer whales are spotted. But what they think is a young killer whale turns out to be a great white shark.

Orcas are at the top of the food chain, but it is unprecedented that they would go after a great white shark. From the boat, whale watchers and experts alike are shocked by what they see.

Why would a killer whale go after a great white shark? Enter Alisa Schulman-Janiger, a biologist who is very familiar with the different families of killer whales off the coast of California.

So if an orca attacking a shark is so rare, how do they usually behave? In this segment, we learn about how orcas around the world live and hunt.

Some orcas do prey on sharks, but how do they do it? Researchers also have to catch sharks occasionally, and there is a particular technique that they use.

The phenomenon of tonic immobility helps researchers study sharks, but does it also help orcas hunt and kill them?

Here we see a simulation of how the attack happened, and find out what effect it had on the population of great white sharks around the Farallon Islands.

How do sharks communicate? Particularly, how would the sharks around the Farallones all know exactly when to evacuate? Scientists who are working on "shark repellent" may have an explanation.

Although no one will ever be completely certain why it occurred, many things have been learned about both species from the attack.

National Geographic filmed South African penguins in their natural habitat. One penguin turns to crime in order to furnish the nest and keep his mate happy.

How does a volcano actually form? This informative video on the topic is brought to you by National Geographic Kids!