Sounding natural does not mean improvising from nothing. The problem usually appears when a candidate memorizes sentences instead of preparing the ideas underneath them.
1. Memorize components, not sentences
Know the decision, two or three pieces of evidence, the trade-off, and the result. Let the wording change from attempt to attempt. That preserves substance without turning the response into a recital.
2. Vary the repetition
If every practice attempt sounds identical, the rehearsal may be training recall rather than interview performance. Answer the same underlying competency three ways: concise, example-first, and decision-first.
If changing one phrase causes the whole answer to collapse, the response is probably stored as a script rather than understood as a reasoning structure.
Answer once without polishing the sentence.
Focus on a clear point, specific evidence, and a defensible reason. Let the wording be imperfect.
3. Review the delivery after the reasoning
Fix substance first. Then reduce long setups, repeated filler, rushed endings, and unnecessary formality. Natural delivery becomes easier when you are not using delivery tricks to compensate for an unclear answer.
Practice rebuilding the answer.
Use the simulator to see whether the same reasoning survives when you have to speak instead of reread your preferred wording.