Sickle and liquid-propellant rocket engine: what they have in common

1. Step 1. Sickle — evolved into — Reaper. Mechanical reaping.
2. Step 2. Reaper — has part — Crank. A crank moves the knife.
3. Step 3. Crank — is part of — Mangle. A handle.
4. Step 4. Mangle — evolved into — Washing machine. Early machines had rollers for wringing.
5. Step 5. Washing machine — has part — Centrifugal pump. A drain pump.
6. Step 6. Centrifugal pump — is part of — Liquid-propellant rocket engine. Turbopumps deliver the propellant.

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