Why was chapter 3 important?

Once again, thunder plays a symbolic role in Cassie's world. On the morning of the incident with the schoolbus, the children set off with sun behind the clouds, only to have the weather change quickly. "Soon the thunder rolled across the sky, and the rain fell like hail upon our bent heads." The seemingly unpredictable changes in the weather mirror the children's seeming luck in escaping the bus. The hope for sunny weather is dashed when the thunder storm begins just as the children's hopes of escaping the schoolbus where the gully is smallest are dashed when they end up jumping into the muddy gully. Thunder, buses, trains, and cars are motifs that play through the entire book.