First act - there is gun.
Second act - plot develops.
Third act - rifle shoots.
Rifle of Chekhov
Hanging on wall, foreboding
Fate yet to be sealed
Gun of Chekhov's play
Foreshadowing the events
Irony ensues
http://tvtropes.org/pmwiki/pmwiki.php/Haiku/ChekhovsGun
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First act - there is gun.
Second act - plot develops.
Third act - rifle shoots.
Rifle of Chekhov
Hanging on wall, foreboding
Fate yet to be sealed
Gun of Chekhov's play
Foreshadowing the events
Irony ensues