Lawn mower and rock drill: what they have in common

1. Step 1. Lawn mower — uses — Wedge. The blades cut grass like scissors.
2. Step 2. Wedge — is used in — Chisel. The cutting edge is a wedge.
3. Step 3. Chisel — is used in — Tunnel. Hezekiah’s Tunnel was cut by hand with chisels.
4. Step 4. Tunnel — uses — Rock drill. Driving the Mont Cenis tunnel.

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