I left out the Korean preference for eating it alive.
Cooking and Preparing Octopus:
Octopuses have an enjoyable mild flavour, with a texture similar to that of squids, though more dense.
Prepare the fresh octopus for cooking. Cut off the eyes and beak. Use the opening to turn the head inside out and remove the ink sac and intestines. Rinse the entire octopus under warm running water for one minute.
Cook octopus quickly over a high heat or simmer slowly. Marinating will help to tenderise the flesh and strengthen the flavour for enhanced results when cooking quickly.
Octopus is tough at the best of times. Among octopus-cooking cultures, there are all sorts of recommendations for tenderizing it.
Greek Style is to beat it against a smooth rock or throw it onto a cement path 100 times, then rub it on the rock in a circular movement sprinkling it with seawater until the tentacles become curly or the membrane between them can be easily torn. Many Octopus that you buy prepared have been placed in a cement mixer with rocks for several hours!
Spanish Style is to dip it into boiling water three times, then cook it in a copper pot.
Italian cooks boil it with a cork (it is believed that enzymes in the cork tenderise the octopus)
The Japanese beat it with mallets.