Hook spur and headphones: what they have in common

1. Step 1. Hook spur — is part of — Spear-thrower. A hook against which the dart rests.
2. Step 2. Spear-thrower — uses — Spear. It throws darts.
3. Step 3. Spear — evolved into — Fire lance. The fire lance was a spear with a tube of gunpowder — the first step to firearms.
4. Step 4. Fire lance — is made of — Paper. The barrel of a fire lance is a paper or bamboo tube.
5. Step 5. Paper — is material for — Loudspeaker. The cone is paper.
6. Step 6. Loudspeaker — is part of — Headphones. Miniature drivers.

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