I volunteered at the Seattle Aquarium for a short stint when I first moved to Seattle (I used to dive a lot and almost became a marine biologist instead of a computer dude.) During orientation, I heard an amazing story about how the staff were finding dead sharks in the big tank. Their tails had been torn off and their guts sucked out, leaving only the skin.
Turns out the octopuses in the tank were snaring the sharks as the the sharks swam past. Well, now, someone has caught this action on video. It's absolutely amazing and more than a little scary, especially as someone who has done night dives with octopi. Check it out.
Those octopuses are super smart. The Seattle Aquarium staff also told a story about how the octopuses adapted to having divers in the tank doing feedings. The octopuses realized that the divers were handing out food every day and wanted to get closer to the action. They quickly figured out the easiest way was to slide up the glass, slide along the surface of the water and find the air hose the diver was using, and then slide down the airhose to the diver. Apparently, the first time this happened, the visitors were watching an octopus come down the airhose toward the oblivious diver. They gestured wildly to the diver, who thought the visitors were waving at him. He smiled and waved back. All of a sudden, the octopus, now on the diver's back, reached around the diver on both sides and started grabbing at the food he was handing out. Obviously, the diver freaked out and shot for the surface. That would definitely make me hang up my dive fins.
I think it's time to declare a truce with the octopuses: we won't eat you if you don't eat us.
Thanks to TEDBlog for the link.