There is something very strange about octopuses -- they are unlike almost all animals we know, and they creep me out because I can easily imagine that the extraterrestrial species that will someday invade and takeover Earth (...) will be very octopus like. (A bit like the aliens in the remake of The War of the Worlds, the one with Tom Cruise, but worse.)
Anyway...they seem even spookier because there's something going up in their brains. This recent Boston Globe piece by Emily Anthes discusses their intelligence, and has a nice graphical guide to some of their shenanigans. Foremost among their tricks hiding themselves in coconut shells, that they carry around with them. By any definition, that's pretty clever.
Here's a video showing how they do it:
It's easy to anthropomorphize animals, but it's become clear, I think, that it's very easy to underestimate them as well. The "intelligence tests" we subject them to look more for our type of intelligence than theirs.