Meet the Giant Pacific Octopus

 With a radial arm span (they're arms, not tentacles!) of well over 20', the Giant Pacific Octopus (Enteroctopus Dofleini) is an amazing creature. Though larger specimens have been reported, the official world record tops 300 pounds, and a 32-foot arm span. To put that into perspective for those of you who are unimpressed, that's the same weight as a freakin' BLACK BEAR! And TWICE the height of a giraffe! Certainly NOT something you wanna mess with.

According to Wikipedia:

Giant Pacific Octopuses are commonly kept on display at aquariums due to their size and interesting physiology, and have demonstrated the ability to recognize humans that they frequently come in contact with. These responses include jetting water, changing body texture, and other behaviors that are consistently demonstrated to specific individuals. They have the ability to solve simple puzzles, open childproof bottles and use "tools". The octopus brain has folded lobes (a distinct characteristic of complexity), visual and tactile memory centers. They have about 300 million neurons. They have been known to open tank valves, disassemble expensive equipment and generally wreak havoc in labs and aquariums. Some researchers even claim that they are capable of motor play and having personalities.

Not only do they have big parrot-like beaks in the middle of their bodies, the salivary gland is full of venom called cephalotoxin. It's paralytic and digestive in nature, designed to paralyze clams and force them to open their shells. While not fatal to humans, it will cause nausea and pain, forming a lesion where the bite happened (which I have on good authority hurts like HELL).

Oh, yeah... they also have ink like a squid. Looks terrifying, doesn't it?