Lock and key and plough: what they have in common

1. Step 1. Lock and key — evolved into — Smart lock. An electronic lock.
2. Step 2. Smart lock — has part — Servomotor. A bolt actuator.
3. Step 3. Servomotor — is part of — Prosthetic limb. Bionic prostheses have motors.
4. Step 4. Prosthetic limb — is made of — Leather. It was attached with leather straps.
5. Step 5. Leather — is material for — Horse collar. The collar and traces are leather.
6. Step 6. Horse collar — is used in — Plough. The horse collar made ploughing with horses possible.

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