Axe blade and refrigerator: what they have in common

1. Step 1. Axe blade — is part of — Axe. A wedge-shaped blade.
2. Step 2. Axe — is made of — Stone. A Neolithic axe is ground stone on a handle.
3. Step 3. Stone — is material for — Ice house. Ice houses were built of stone and sunk into the ground.
4. Step 4. Ice house — evolved into — Refrigerator. The refrigerator replaced natural ice.

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