I don't know whether this is true of Iron Chef Japan, but I have a vague memory of an Iron Chef America contestant once leaking the info that the two teams (which, hmmm, as an aside, makes me think that the Iron Chef choice is not a last-minute thing either) are told in advance that the secret ingredient may be one of two things. Chocolate or flounder. Avocado or Kobe beef. Pork or apples. Fennel or duck.

I don't know if it's true, but if it is, it suggests that each team is wise to plan for two sets of dishes in advance. It also explains (to me, at least) something about the looks on their faces when they see the secret ingredient unveiled, and their quickness in going about preparing dishes for that ingredient.