In the first sentence of this section, the fire at Montag's house is described as a "carnival." What does the use of this word show you about Montag's neighbors?

It shows they were all trying to witness what was happening

Explanation:

In the text is established that everyone was turning on their lights to see what was going on.

Carnivals are parades with thousands of people all watching a show, there are a lot of lights and even fire for some shows.

This description compares the neighbors to the spectators in a carnival, compares the houses to the lights and establishes the fire as the main show.

It is described as a carnival because everyone was stepping out of there house to watch his house burn down. This is similar to when you go to a carnival. Everyone is standing around watching.