Titus is unable to concentrate at School™ where there have been funding cuts lately (no more school band, and only living teachers). He doesn’t reply to Violet, just listens to her message again and again. He stares at his hologram teacher, who looks “just like an empty shell.”
In Part Four, there are various subtle signs that the U.S. is falling apart—the school system is collapsing (even though, supposedly, it’s supported by all-powerful corporations). The image of an empty shell is an apt way to characterize Titus’s hollow, apathetic emotional state.