Octopus in case that is frozen is thawed in cold water. Once defrosted put to boil water in a large saucepan - it takes about 15 liters. In water, put the chopped lemons, salt and vinegar. Carefully submerge 2-4 cm from the tentacles of the octopus in the boiling water, hold 10-15 seconds and remove, then dipped 6-8 cm and also keep a few seconds in the water and move away, so proceed until immerse the whole octopus. The aim is always to boil water, and if you put immediately into the water octopus will remain tough. When submerged the whole octopus boil exactly 15 minutes. It takes away from the fire and leave the court about 12 hours. After washed with cold water, and cut into thin slices of about 1 cm. Cleaned a few stalks of celery and cut into small pieces, add to the octopus, seasoned with a little salt, pepper, juice of 2 lemons, finely chopped garlic and olive oil. All mix well and leave for 1-2 hours to blend flavors. Serve as an appetizer.