The question is incomplete and the full version can be found online.
Answer:
To emphasize the seriousness of what is about to happen.
Explanation:
In "Big finish," by Erin Michelle Jendras, when the woman on the screen gets quiet as soon as the numbers get to ten, she does so because it´s time for the final countdown. As soon as the count gets to zero, the reader will discover that Terra, the planet earth humans had to escape years before, is being destroyed. The sudden silence of the woman broadcasting the live event is a small detail that makes it clear that what´s about to happen is an important event.
