Idiom meaning, usage examples, facts

1. This heatwave is killing me. I'm sweating like a pig.
2. Then you don't have to stand there sweating like a pig.

The origin of this idiom is difficult to source. It is strange to include a pig's reference in this phrase, as pigs don't have any sweat glands and cannot perspire in this way. Some believe that this idiom stems from the smelter of pig iron, which at a critical stage of manufacture, when cool enough to transport, "sweats."