Horseshoe nail holes and tunnelling shield: what they have in common

1. Step 1. Horseshoe nail holes — is part of — Horseshoe. Horseshoe nails fix the shoe.
2. Step 2. Horseshoe — uses — Nail. It is nailed on.
3. Step 3. Nail — uses — Wedge. The point of a nail pushes the wood apart.
4. Step 4. Wedge — is used in — Chisel. The cutting edge is a wedge.
5. Step 5. Chisel — is used in — Tunnel. Hezekiah’s Tunnel was cut by hand with chisels.
6. Step 6. Tunnel — uses — Tunnelling shield. Shield tunnelling.

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