Twist ending
An unexpected ending that overturns the reading of the whole text — the short story's specialty, from Maupassant to O. Henry.
The twist ending surprises and, in its purest form, forces a rereading of everything before it in a new light: the necklace was fake, the narrator was dead, the hunter was the prey. It's the short story's queen closing figure — Maupassant in French, O. Henry in English made it a signature.
The law of the twist is fairness: all clues must have been given, no direct lie told. Surprise springs from misdirected attention, not from disloyally hidden information. A fair twist produces the characteristic double pleasure — surprise, then retrospective obviousness: "it was all there."
Example
O. Henry's "The Gift of the Magi": each spouse sacrifices the very thing the other's gift was for.