A mysterious line of dialog.
A secret suddenly revealed.
A major decision or vow.
Annoucement of a shattering event.
Reversal or surprise - new information that tuns the story around.
A question left hanging in the air.
He also says, “If a scene seems to sputter to a close and you’re not sure what to do, here’s a great tip: try cutting the last paragraph or two. You don’t have to write ever scene to its logical conclusion ... cutting creates interest, a feeling of something left hanging - and that makes readers want to find out why."