Exchange
You count with your fingers in prison all of the mouths and legs you've acquired. Soon you'll be able to make a big exchange with all of these body parts to get something awesome.
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You learned this type of exchange from the mighty Genghis Khan (かん). You read a book or watched a show about him once and you're pretty positive that Genghis Khan would exchange the body parts of his enemies all over the continents of Asia and Europe for nicer stuff.