Octopuses are extremely intelligent................
Just like dolphins 🐬 and primates.
Octopus have a relatively large brain mass but it's divided up between nine sub-brains (actually just clumps of neurons). Each of the eight arms (not legs and not tentacles) has its own independent sub-brain. The eight "arm brains" make up 2/3rd of the total brain mass.
The central "brain" will send a command to an arm and then turn its attention to other matters while the arm performs the task independently. Like tell the arm, "pick up that clam shell," then while the arm is doing that, the main brain focuses on the stingray that looks like it might be trying to sneak up on it. And the arm will complete the task without any further input from the central brain.
The arms need all that brain power because not only do they act independently, it is the most flexible, most intricately-controllable limb in the animal kingdom. About a thousand times more intricate than an elephant's trunk (which also has not bones). Plus, the arm's suckers are incredibly powerful and complex sensory organs. They have a sense of touch that's dozens of times more sensitive than a human, plus the suckers can smell and taste. And a single arm can have upwards of 300 suckers. The octopus can run its arm down into a hole it can't see into in search of food, and by feeling around tell everything it needs to know about what it discovers, sight-unseen.
I've been on scuba dives with people who found a "playful" octopus that tolerated the diver's presence and even felt of them for some time. Back on the dive boat they're all giddy because the octopus was being friendly with them. I love the look on their face when I tell them, "No, it wasn't making friends, it was tasting you, to find out if you'd be worth killing and eating."
They also can shed an arm as a defensive measure and the discarded arm will continue wriggling to distract the predator. And the sacrificial arm grows back in two or three months.
They're far the most intelligent invertebrate. They can recognize and remember individual humans to the extent of "picking on" people they don't like. A researcher kept a captive octopus in his home and hung a bell over the tank and dropped the bell cord into the water. The octopus learned to use the bell to summon a companion when it wanted attention.
They display problem solving, tool use (but as yet haven't been observed making tools), planning for future eventualities, and they use deception as a hunting tactic.
Possibly the most amazing part is that most octopus only live about two years. The Giant Pacific octopus commonly will live four but most of the rest are only good for two.
So how do they get to be so smart so fast?
Probably more intelligent than much of Congress.