I once read about a lab that was doing research on various sea creatures, but primarily crabs. The experiment involved having 100s of a certain type of crab. Every day the crabs were counted, and each day there was quite a few completely missing. The head researcher suspected one of the lab assistants was stealing and selling the crabs, so they set up a camera to watch the lab overnight. It turned out that it wasn't one of the assistants, but instead the lab's octopus. Every night it was waiting until everyone went home, then taking the lid off it's tank, crawling several meters across the floor, opening the lid of the crab tank, eating a few crabs and then crawling back, remembering to replace the lids of both tanks.
