Wooden shield planks and electric motor: what they have in common

1. Step 1. Wooden shield planks — is part of — Shield. The backing.
2. Step 2. Shield — has part — Handle. A grip behind the boss.
3. Step 3. Handle — is part of — Toothbrush. A plastic handle.
4. Step 4. Toothbrush — evolved into — Electric toothbrush. A motorized toothbrush.
5. Step 5. Electric toothbrush — has part — Electric motor. A small motor.

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