Sperm whales have the largest brains of any animal that has ever lived on Earth. There's more to intelligence than just brain size, of course, although it's hard to believe any animal with an 18-pound brain doesn't have a lot going on upstairs. But since sperm whales are elusive and often spend long periods of time in the deep ocean, the most our 3-pound brains can do is wonder.

Well, most of the time, anyway. Sometimes these bulky brainiacs offer us a brief window into their lives, and in rare cases they even develop a rapport with us — which is generous, considering our species' grim history of harpooning them. One of the lucky humans to be trusted by sperm whales is Andrew Armour, a diving guide in Dominica appropriately nicknamed the Whale Whisperer.

Armour recently showed off that relationship while guiding a tour group that included Scott Belt, an underwater photographer who captured the video above. It not only shows Armour swimming alongside a huge sperm whale, but also performing spin moves the whale is clever enough to mimic. While captive orcas are notoriously forced to perform tricks at some theme parks, Armour points out this is a wild whale that could swim away if it wanted. Instead, it seems to be having fun.

"The performance of spinning and getting them to do likewise is simply from my idea that they should also be enjoying the interaction, and that is what makes what I do so successful," Armour tells BT.com, a British news website. "These animals have been spending great lengths of time off Dominica's west coast. This means that I have been able to do quite a bit of interaction with these whales from the time I started swimming with them in the early '90s."

Armour's tour group didn't know they'd get to see this, Belt adds, and they could barely believe it.

"I was completely surprised by what I was witnessing in person and capturing on video; there was no advanced plan that the guide would try to get the whale to react," Belt tells BT.com. "It was almost unbelievable to see the whale's response by spinning along with the guide."

Belt released his video to Caters News Agency, which posted it to YouTube under the title "Whale Spins on Command of Diver." As one commenter noted, though, "a quick analysis of the power dynamic in that situation would indicate you should replace 'command' with 'request' ;)"

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Russell McLendon ( @russmclendon ) writes about humans and other wildlife.