We’ve all been lied to and we’re here to remedy the falsehood. You think you’re “sweating like a pig”, do you? PIGS CANT SWEAT! The term is actually derived from the iron smelting process in which hot iron poured on sand cools and solidifies generating a sow and piglets. Hence "pig iron". As the iron cools, the surrounding air reaches its dew point, and beads of moisture form on the surface of the "pigs". "Sweating like a pig" indicates that the "pig" (ie iron) has cooled enough to be handled. Since you slept through ninth grade science just buy a Pigs Visor to cool your hot head and call it a day.