Sisal fiber board and optical telegraph: what they have in common

1. Step 1. Sisal fiber board — is part of — Darts. Compressed fibre that holds the darts.
2. Step 2. Darts — evolved from — Bow and arrow. Accuracy of shooting.
3. Step 3. Bow and arrow — evolved into — Crossbow. A bow on a stock.
4. Step 4. Crossbow — has part — Trigger. A trigger.
5. Step 5. Trigger — uses — Lever. A lever mechanism.
6. Step 6. Lever — is used in — Optical telegraph. The arms were moved by a system of levers and rods.

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