So, this aquarium moved a large octopus into a bigger tank, assuming that its strength and stealth would keep it safe from the other critters in the new environment — a population that included sharks in the 3 to 4 foot range.
Something weird happened. They kept discovering shark carcasses at the tank bottom each morning, so they stayed up to see what happened (link to embedded RealVideo at PBS). As it happens, the shark turns out not to be the indisputed food chain king in this particular tank. (Link via MeFi.)