Burglar alarm and knife: what they have in common

1. Step 1. Burglar alarm — has part — Electromagnet. A bell.
2. Step 2. Electromagnet — uses — Electromagnetism. Current creates a magnetic field.
3. Step 3. Electromagnetism — is used in — Starter motor. A starter is an electric motor.
4. Step 4. Starter motor — evolved from — Crank. It replaced the starting crank.
5. Step 5. Crank — is part of — Meat grinder. A handle.
6. Step 6. Meat grinder — has part — Knife. A cross-shaped blade.

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