Sweating like a Pig

The term "Sweating like a Pig" denotes perspiring profusely. 

I can't recall the source of this and therefore my apologies to the author but this was what I recently found out about the saying.  

"This sounds illogical, as pigs have ineffective sweat glands, but the term is allegedly derived from the iron smelting process. After pouring into runners in sand, it is allowed to cool and is seen as resembling a sow and piglets, hence "pig iron". As the pigs cool, 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 has cooled enough to be moved in safety. "