Octopuses, while kinda creepy, are supposedly one of the most intelligent invertebrates. They can apparently solve problems, figure out complex ways to get at food (including opening jars!) and have one of the most sophisticated eyes in the animal kingdom. Probably why you get that creepy feeling, looking at their eyes.
Anyway, I found a video of shark getting eaten by an octopus. Well, gotta shelve those scuba diving plans :)