In the nose of a salmon there is a piece of cartilage so clear it looks like ice. The word for it, hizu, is written with the character for ice. It is shaved thin, dressed with vinegar and grated daikon, and it makes a small dry sound against the teeth that no other part of the fish makes.

There is very little of it. A five-kilo salmon yields perhaps fifty grams, which is why the dish belongs to New Year and to celebrations rather than to Tuesday. It is made from a part that would otherwise be discarded, and it is nevertheless not everyday food, a contradiction that seems not to trouble anyone.

It is old. A court compilation of 926 lists hizu among the goods sent up to the capital, which means people were eating this several centuries before the country had a shogun. Salted salmon made it portable, so the dish spread inland long before refrigeration. Miyako, on the Sanriku coast, lands more autumn salmon than almost anywhere on the main island, and the Tsugaruishi river fills with fish climbing it every year.

A thousand years of eating the very tip of a fish's head. Somebody worked out that it was worth the trouble, and then nobody stopped.