In underwater footage, a marine biologist is seen apparently interacting with an octopus during crab hunting. The video, shot in the waters of the Great Barrier Reef off the coast of northeastern Australia, is a snippet from the upcoming National Geographic documentary series “Octopus Secrets.”

The three-part series, created by director James Cameron, follows marine biologist Alex Schnell as she explores the secret lives of these unusual and elusive creatures, whose significant intelligence becomes increasingly evident.

“Cephalopods (the group of animals that includes octopuses, squids, and related creatures) have always been of interest from a very young age,” Schnell told Newsweek. “They’re so alien — they have three hearts pumping blue blood, no bones, and skin that can change color in the blink of an eye. But within this truly strange structure, we see glimpses of intelligence.”

For the series’ filming, the team spent two years underwater and nearly 1,500 hours documenting the behavior of octopuses in 10 different locations across five countries, including Canada, Indonesia, Australia, Brazil, and the Turks and Caicos Islands.