Processed fish

Salt cod is cod (or any whitefish) that is salted and dried for preservation. Prior to refrigeration, salt cod was one of the most widely eaten fish in the Western world. It resembles shoe leather, and in order to eat it, it must be soaked to reconstitute it.
The Norwegians, not ones to toe the line, chose to reconstitute their salt cod with lye instead of water. It is not entirely clear who came up with the idea of using lye (which they knew was dangerous), but it was almost certainly an accident.
Truly bizarre, though, is the fact that it caught on. For centuries. Especially when you consider that lutefisk is described (almost universally, although not by the Vikings) as having "the consistency of Jello-O." Or, according to Garrison Keillor, phlegm. Not a ringing endorsement.
And for the final nail in the lutefisk coffin: even my mother won't eat it.