Actually the Japanese used to catch octopus by lowering heavy clay pots into the water and then waiting for them to go inside, sort of like crab fishing but using the pots instead of a net. With these coconut halves, the octopus' are able to carry them away and use them for shelter whenever at will.
There was an article in a local newspaper about this the other day..it's amazing how other species adapt in this world to their changing enviroments.....