The octopus in general, and the nature of its intelligence in particular, remain a mystery in many ways. This great rundown of what we know includes lots of lovely footage of these delightful creatures.
And one more thing, there was recently a report about the tendency for an occasional octopus to punch a fish now and then. I wasn't super-happy with how this was presented, because many reports anthropomorphized our 8-legged friends, saying it was for "no reason." That concept is very anthropocentric, as empathy and impulse control are probably not well evolved among octopodes. So while it's OK to wonder why Marquis Ventura blasted Rick Moranis and several others in the face for "no reason," an octopus is probably behaving that way for a different set of reasons.
Image: YouTube / Real Science