LitCharts assigns a color and icon to each theme in Cat’s Cradle, which you can use to track the themes throughout the work.
Science and Morality
Religion
Governance, Politics, and Nationhood
Absurdity and Meaninglessness
Summary
Analysis
Dr. Breed tells John about Dr. Hoenikker’s proposed solution to mud: ice-nine. This is a substance which can make water crystallize at an atomic level. A “seed” of the substance makes atoms “stack and lock” and freeze. Dr. Breed’s explanation is interrupted by the Girl Pool singing “O Little Town of Bethlehem.”
Essentially, ice-nine can make water freeze without it needing to be at a low temperature. The interruption is absurd, the harmless carol contrasting with the potentially world-changing implications of ice-nine.