The narrative technique that the author is using is pacing. By using shorter sentences and more punctuation in the rising action and climax of the short story, the author is creating a faster pace that makes the reader feel like the story is moving quickly. This technique is commonly used in action scenes or suspenseful moments to create tension and keep the reader engaged. By changing the pace of the story, the author is able to manipulate the reader's emotions and create a more impactful reading experience.