Headphones and petri dish: what they have in common

1. Step 1. Headphones — uses — Sound wave. The diaphragm creates a sound wave.
2. Step 2. Sound wave — is used in — Whistle. The sound of a flow.
3. Step 3. Whistle — is part of — Whistling kettle. A whistle.
4. Step 4. Whistling kettle — is a kind of — Kettle. A kettle.
5. Step 5. Kettle — has part — Pot lid. A cap.
6. Step 6. Pot lid — is part of — Petri dish. A cap.

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