LitCharts assigns a color and icon to each theme in The 5th Wave, which you can use to track the themes throughout the work.
Trust and Belief
Survival and Perseverance
Warfare and Dehumanization
Family
Summary
Analysis
Cassie, Ben, and Sammy narrowly squeeze through some debris on the stairs.
Squeezing through the debris is another example of how Cassie and the others are like cockroaches, small but capable of surviving and getting through tight situations.