Pressure fuze and stone tool: what they have in common

1. Step 1. Pressure fuze — is part of — Landmine. Triggered by pressure.
2. Step 2. Landmine — uses — Gunpowder. Chinese mines of the 13th century were filled with gunpowder.
3. Step 3. Gunpowder — is used in — Fire lance. A gunpowder charge.
4. Step 4. Fire lance — evolved from — Spear. The fire lance was a spear with a tube of gunpowder — the first step to firearms.
5. Step 5. Spear — has part — Stone tool. Early spearheads were made of stone.

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