For cannibals, octopuses seem to be surprisingly fun loving.

Some have been observed using their funnels to repeatedly blow objects around in their tanks. Others, such as one common octopus named Dorian, have spent a countless minutes passing Lego blocks around among their many arms or towing them back and forth across the surface of the tank.

After careful study and deliberation, researchers decided there was really no good reason—food, safety or reproduction—for octopuses to be doing these things. The octopuses were instead doing something rather surprising.

They were playing.

Such complex behavior might seem impressive for a mere mollusk. But, as we are learning, the octopus nervous system is a masterful—if still partially mysterious—solution to life in the fast-moving ocean. Especially when you don't have a shell or a carapace to hide inside of (clams and lobsters, I'm looking at you).

These investigations and many others are described in the new book Cephalopod Cognition (Cambridge University Press, edited by Anne-Sophie Darmaillacq, Ludovic Dickel and Jennifer Mather). In it nearly two dozen of the world's leading experts on octopuses, squid, cuttlefish and nautiluses come together to share fascinating tales of surprising behavior—and what we are learning about the detailed physiology behind it.

After swimming with the octopuses—literally, although mostly figuratively—for more than four years now, as a non-expert, I feel relatively well versed in their oddities. But this book has opened my humble human eyes (blemished, unlike those of an octopus, with a blind spot) to many new astounding facts—and exciting avenues for future study.

Not to mention many questions I had never before pondered. Such as: Why do squid eyeballs get bigger and then smaller with ocean depth?

If you're the slightest bit intrigued by these weird invertebrates, you can hardly do better than to be in the capable hands of this volume's contributors.

And you might just learn something about the evolution of our own brains in the process.

Learn more about the inner world of surprisingly smart cephalopods in Octopus! The Most Mysterious Creature In the Sea, which is out now in hardcover and available for pre-order in paperback (ships November 25th).

Illustration courtesy of Ivan Phillipsen