Answer:
"But it's not a pretty sight."
Step-by-step explanation:
A euphemism is a mild, indirect, or polite word or expression used to replace another word or expression that is considered unpleasant, offensive, blunt, or harsh. The Captain uses a euphemism when he refers to the atomic fission he saw saying “it's not a pretty sight,” to avoid using a harsh and unpleasant expression that would describe the shocking and serious event.