The Napolitan tale, originating around 2003 on Japanese message boards, lets a seemingly ordinary restaurant anecdote resolve — through homophonic wordplay — into something monstrous, such as cannibalism. It never shows directly; the reader assembles the meaning.
Building horror by implication alone, the form shares the grain of the unnameable and of observational ambiguity.
The form keeps a few rules most of the time. The setting has to be an ordinary day that could happen anywhere, one or two details out of place are enough, and the narrator ends the account without ever having understood what happened to them. The moment a single explanatory sentence goes in, the piece turns into a different kind of writing.
Another mark of the form is that the reader’s own attempt at a solution belongs to the work. Once a tale is posted to a board, competing readings gather beneath it and none of them is ever settled. That nobody knows the answer is the story’s last device.
This is what separates it from the “scary once you get it” riddle tale. There the solution resolves into one and the story closes at that moment; in a Napolitan the readings stay plural and none of them closes. In Korea the name has been taken up more broadly, and now covers any story that leaves an uneasy residue you cannot account for.