Another measure of intelligence: you can count neurons. The common octopus has about 130 million of them in its brain. A human has 100 billion. But this is where things get weird. Three-fifths of an octopus's neurons are not in the brain; they're in its arms. [...]
"I think consciousness comes in different flavors," agrees Mather. "Some may have consciousness in a way we may not be able to imagine."
It's an enchanting read, filled with moving descriptions of the author's and others' interactions with Athena, a giant Pacific octopus. For example:
The way she held Menashi with her suckers seemed to me like the way a long-married couple holds hands at the movies.