Vaccine and centrifugal pump: what they have in common

1. Step 1. Vaccine — uses — Syringe. Injections.
2. Step 2. Syringe — works like — Piston pump. A syringe is a hand-operated piston pump.
3. Step 3. Piston pump — is part of — Fire pump. A fire pump is a piston pump.
4. Step 4. Fire pump — evolved into — Fire truck. A pump on a motor-vehicle chassis.
5. Step 5. Fire truck — has part — Centrifugal pump. A fire pump.

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