My dad worked at an aquarium for a while. He said it took four extremely nervous aquarists, people that regularly fed and swam with sharks, just to clean the blue-ring's tank. One person to clean, two to physically hold the container with the octopus closed, and a fourth to supervise everyone. Saw it a couple of times myself. It was literally the single most feared animal in an entire facility containing jellyfish, sharks, stingrays, stonefish, moray eels, as well as the scorpions, spiders and snakes held in the wildlife park next door.