A seaweed called egonori is boiled until it dissolves, then poured out and left to set in a flat sheet. Sliced, it is greyish and faintly translucent, with the give of something between jelly and paper. It is cut into short strips, and bonito flakes, grated ginger, spring onion and ground sesame go on top, then soy sauce or vinegared soy. That is the whole preparation.

The name is written several different ways, and each spelling carries its own story. One reads as sea-udo, from the notion that the seaweed shoots up the way the udo plant does. Another reads as the people of the offing. A third reads as the rescuer of people, and is attached to a famine, when the stuff is said to have kept a coastal population alive. Nobody has settled the question.

Before the war, in Hakata, sellers walked the streets with it at first light, the way other cities had men selling natto or clams. They timed their rounds to reach households while breakfast was being laid.

It tastes of almost nothing on its own. What you taste is the soy sauce and the ginger. And still there are people here who have eaten it before work, most mornings, for their whole lives, and who would notice at once if it were missing.