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
Tank gets sent away for a psychiatric evaluation. One day, Dumbo, who is training to be a medic, calls Zombie over and shows him that one of the cadavers he’s training on is Tank. Dumbo can’t figure out a cause of death.
Tank’s death is highly suspicious and seems to confirm the rumor Zombie heard earlier that people who act out have a way of conveniently dying by suicide. The implication, though, is that these people have been murdered. This is a turning point that causes Zombie to begin to question his training.