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

1. Step 1. Kettle spout — is part of — Kettle. A drain.
2. Step 2. Kettle — evolved into — Electric kettle. A kettle with a heater.
3. Step 3. Electric kettle — has part — Heating element. A heating element in the base heats the water.
4. Step 4. Heating element — is part of — Dishwasher. Heating the water.
5. Step 5. Dishwasher — has part — Centrifugal pump. A pump feeds water to the spray arms.
6. Step 6. Centrifugal pump — is part of — Liquid-propellant rocket engine. Turbopumps deliver the propellant.

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