Fast. Organized. Rapid scenes with no elaborate set ups. The story is unraveling. Up to this point, your hero has been tested, tried everything, but only has one way left, propelling him head on into a new confrontation with the inevitable.
But throughout the second act, your hero has been changing, learning, and developing. This is his CHARACTER ARC. And that change begins to manifest in the third act, often sparked by the Main Culmination and fueled from the NEW TENSION introduced. Simply put, your character learns the lessons in Act Two, but in Act Three he must now apply that knowledge, and the person he was in the beginning is clearly not the same person now.
One way to test this change comes in the form of the Third Act TWIST, a surprising, yet explainable change in the direction of the action of the storyline and new third act tension.