Nigorobuna, a carp found only in Lake Biwa, is packed in salt for two or three months. It is then washed, dried, layered with rice in a barrel and put under a weight. When the lid comes off, the smell arrives first, and for anyone meeting it new, the smell is considerable.

This is sushi in its oldest form, from before vinegar entered the story. The souring is done by lactic fermentation, slowly, in the dark, so no vinegar is needed and none is used. Sliced, the flesh is amber and faintly damp, and a single thin piece on the tongue is far quieter than the smell has led you to expect. People reach for cheese as a comparison, and they are not wrong, though the comparison stops being useful after about a second.

What it really is, though, is a lake preserved by the houses beside it, using nothing but salt, rice and time. Refrigeration arrived in these villages within living memory. The knowledge that came before it is still here on the plate. The fermentation slows through the cold months and the fish is ready around New Year, by which time the bones can be eaten, and the rice is served alongside rather than thrown away.

People divide cleanly into those who stop after one slice and those who reach for a second. There does not seem to be a third group, and almost nobody manages to stay neutral about it.