Rabies vaccine and sickle: what they have in common

1. Step 1. Rabies vaccine — is a kind of — Vaccine. A vaccine.
2. Step 2. Vaccine — uses — Syringe. Injections.
3. Step 3. Syringe — has part — Needle. A hollow needle.
4. Step 4. Needle — evolved from — Stone tool. Bone needles with an eye are part of the Palaeolithic toolkit.
5. Step 5. Stone tool — evolved into — Sickle. The first sickles had flint inserts.

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