Something mysterious and delightful happens in San Francisco and environs around the holidays. I am not speaking of jolly old elves in little hats and those $#^%& bell ringers out side of Safeway, I refer, of course, to the sweet, juicy, delicious bounty that is the winter Dungeness crab season. Nothing says Christmas or Kwanzaa like ornery little pink alien-looking foodstuffs. This winter kind of sucks because some yahoo went and crashed an oil tanker into the Bay Bridge, causing commercial crab season to be postponed and making the Baby Jesus cry. Because of this, you should call ahead to make sure there is crab available. But when the season officially starts, do what the natives do: stuff yourself silly on these succulent shellfish until you swear you'll never eat one ever again, ever. Until next November, of course.