Here's how I make my octopus franks:
Step 1: Take a frankfurter and cut it into half. I find shorter, thin frankfurters work well.
Step 2: Hold the frankfurter vertical with the cut side up. You will see it is circular in shape. Imagine it is like a round pie you are going to divide into eight equal slices. This will form the eight legs of the octopus.
Firstly make a vertical slice down to cut the 'pie' into half. Keep going until you reach about 2/3 of the way down the frankfurter. The remaining 1/3 will form the body of the octopus.
Step 3: Rotate the frank and make a similar vertical slice 2/3 down the frank to divide the 'pie' into 4 equal quarters.
Step 4: Rotate the frank again, and slice down to make six, then eight sections. Take care on these last two cuts as it is easy for the legs to break off here. Try to divide the pieces as evenly as possible so the legs are of equal width. It helps to hold the other pieces together tightly as you slice (watch your fingers, though).
Step 5: Cut two eyes in the body section of the octopus by twisting two small holes into the frank with your knife, a skewer or chopstick. I find a pointed chopstick works well.
Step 6: Boil water in a small pot. Put the franks inside and boil for a few minutes (or follow the instructions for your brand of franks). Watch as the legs magically spread out in the water! Your octopus franks are learning to swim...
Step 7: Once the legs have opened, remove the octopus franks and use them to decorate your bento or any other dish to thrill your kids (or yourself)!
There are several other methods for slicing the legs, but I find this method gives the best control to create legs of even width. Another option is to panfry the franks a little to give them more colour.