Smallpox vaccine and dewar flask: what they have in common

1. Step 1. Smallpox vaccine — is a kind of — Vaccine. The first vaccine.
2. Step 2. Vaccine — uses — Syringe. Injections.
3. Step 3. Syringe — is made of — Silver. Early needles were silver.
4. Step 4. Silver — is material for — Mirror. A silver coating.
5. Step 5. Mirror — is part of — Vacuum flask. The silvering reflects heat radiation.
6. Step 6. Vacuum flask — evolved from — Dewar flask. A household Dewar flask.

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