When hunting for tasty morsels like crabs and scallops, octopuses must watch out for predators at all times. That's why some of these brainy, eight-legged creatures bring along ready-made body armor—sometimes in the form of coconuts.

In a YouTube video (above) that recently went viral, an octopus trudges along the ocean floor carrying two halves of a coconut. Suddenly it stops, pulls them together and climbs inside.

Scientists have known about this behavior for a while, but it was first filmed in 2009 in North Sulawesi, Indonesia, by a team of biologists from Museum Victoria in Melbourne, Australia. (Related: "' Bizarre' Octopuses Carry Coconuts as Instant Shelters .")

"I knew I was seeing something really special, so letting go of the camera just wasn't an option," says Julian Finn , the museum's senior curator for invertebrates, who filmed the 2009 event.

"I just had to do my best to suppress my laughter, keeping my teeth clenched around my regulator and hope that the seawater wouldn't be sucked back into my lungs. While, of course, keeping the camera steady."

Tool Debate

For a long time, scientists thought only people used tools, but ongoing research reveals that other animals do it too.

Though there's no single definition for what constitutes tool use, Finn says the coconut-carrying is an example. That's because the octopuses are gathering and assembling coconut shells with the foresight that they may need them in the future.

But others, such as marine biologist James Wood , are a bit more skeptical.

"My house isn't a tool for me—it's my house," says Wood, who runs The Cephalopod Page, a website focusing on the group of invertebrates that include octopuses, squid, and cuttlefish.

"But if I need a hammer or a screwdriver to put up drywall, that is a tool."

Wood believes a tool is an object used by an animal to interact with and change their environment. (Watch a video of an octopus chasing another octopus.)

"if you're going to say [the coconut-carrying octopus is] tool use, then anything that carries or uses another object for protection would then be using tools," he says. "You have to draw the line somewhere."

But Jennifer Mather , a professor of psychology and neuroscience at the University of Lethbridge in Alberta, Canada, argues octopuses use tools. She's studied how octopuses shoot water jets to clear dens of sand and grit and stack rocks in front of the openings. (See "Journey of Octopus Discovery Reveals Them to Be Playful, Curious, Smart.")

"It's clear that there is no single way of using tools," she says. "It's a fascinating behavior, but it's not a unitary behavior."

Staying Safe

Regardless of where a scientist stands on the tool question, it's indisputable that octopuses are "masters at manipulating and mimicking their environment," says Finn, the biologist who filmed the original coconut-carrying octopus. (" Watch: Stealthy Octopus Leaps From Water and Attacks Crab .")

Unlike mollusks such as clams, octopuses don't have a hard shell to protect them from predators—so they need to be creative to survive. Some change colors to blend into their surroundings with remarkable accuracy, and many more shoot ink when threatened.

As for the coconut-carrying behavior, it could be a way for an octopus to feel safe while it's out in the open, Wood adds.

The octopus in the new video is seen walking exposed on the seafloor—not an ideal locale. Octopuses spend much of their life in lairs, which they dig under coral reefs or fashion in rocky outcroppings.

"They don't starve to death and they don't tend to die of diseases," says Wood the marine biologist. "They get eaten."