Knife and sonar: what they have in common

1. Step 1. Knife — is part of — Meat grinder. A cross-shaped blade.
2. Step 2. Meat grinder — has part — Auger. An auger.
3. Step 3. Auger — evolved from — Archimedes’ screw. The Archimedes’ screw as a conveyor.
4. Step 4. Archimedes’ screw — evolved into — Propeller. The first propellers by Smith and Ericsson were a variation on the Archimedes’ screw.
5. Step 5. Propeller — is part of — Submarine. A propeller.
6. Step 6. Submarine — has part — Sonar. Underwater acoustics.

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