Kettle spout and glasses: what they have in common

1. Step 1. Kettle spout — is part of — Kettle. A drain.
2. Step 2. Kettle — includes — Whistling kettle. A kettle.
3. Step 3. Whistling kettle — has part — Whistle. A whistle.
4. Step 4. Whistle — is made of — Bone. Ancient whistles were carved from bone.
5. Step 5. Bone — is material for — Spectacle frame. The first frames were made of bone and horn.
6. Step 6. Spectacle frame — is part of — Glasses. A frame.

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