Video: Gulp. Just look at how ridiculous this thing looks. It's a giant black sea slug known as a sea hare and it's freaking monstrous. You don't really hold it in your hand as much as the sea hare, which can grow up to over 0.91m long and weigh over 14kg, just swallows your entire arm. Brave Wilderness found the black sea hare in the tide pools off the coast of the Pacific Ocean in San Pedro, CA and described holding it as super slimy and unbelievably slippery.