"The Cyclops’ eye hissed round the olive stake in the same way that an axe or adze hisses when a smith plunges it into cold water"
Odysseus and his men blind Polyphemus, detail of the 'Eleusis Amphora', ca.650 BC
GNU Free Documentation LicenseOdysseus and his men blind Polyphemus, detail of the 'Eleusis Amphora', ca.650 BC - Credit: Napoleon Vier/Wikimedia Commons
When forging weapons, the smith pounds red-hot metal into shape, then plunges it into cold water. The rapid change in temperature helps to make the weapon stronger. The process of reheating and cooling metal to toughen it is called tempering.

 

Watch this video to see a traditional katana (Japanese sword) being forged. Skip to 1:12 for the hiss as the blade is plunged into cold water.