Which phrase from the story
shows that Zarna is excited about
how the water drum worked?

The move over law is for safety of yourself and the officer and the ones pulled over, as a driver pulling over the officer control the situation with the pulled over person.

if it is an ambulance or fire truck with their sirens on it means they are having to get to an emergency so for the others safety for the emergency to save lives, pulling over lets them get through.

i hope this : )