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
The next few moments were a blur for Cassie. She pulled out her hidden pistol and shot Corporal Branch in the head. She was confused and went back toward the camp, a decision she later regretted. When she was there, she heard gunshots. She saw her father bloody and crawling out of the complex. He mouthed that Cassie should go, then collapsed. Cassie hoped he was just playing dead, but then Vosch came out and shot him in the head. Vosch then noticed Cassie and pointed his gun at her.
As Cassie noted, earlier, she isn’t used to thinking of herself as a killer, and so it makes sense that during this first moment of her killing another person (anticipating what she’ll do to the Crucifix Soldier later in the chronology of the story), Cassie feels disconnected from her body. This sense of disconnection that Cassie feels suggests that killing another person requires not just dehumanizing the victim, but also dehumanizing yourself.