The sperm whale's brain is about 6 times the size of ours... They've had it for 15 million year longer... We've had our current size brain around 200… - James Nestor

[T]he lowest recorded heart rate [of a free diver]... was 7 beats per minute... about 1/2 of someone in a ...

[I]n many ways, rocks at the bottom of the deep sea, buried under a mile of Earth’s crust, or covered in bird crap on aren’t inanimate objects at all. They are undulating, "breathing" systems crammed with organisms so tiny and metabolizing so slowly that nobody ever noticed.
Most researchers never bothered. Seeking out extreme life requires traveling to some of Earth’s most far-flung and miserable environments. Only a handful of microbiologists and geologists have had the will, fortitude, and resources to endure weeks in the triple-digit heat within African mines, or months in the frozen expanses of Antarctica, or years sifting through the polluted oil fields of to find answers.

I found out later that these clicks are actually used for communication. These animals also use them to see in the deep ocean. ...It's a form of called echolocation.