Excursion into Vulgarity...

…does anyone know the origin of the rustic expression “I didn’t know whether to shit or go blind”? It seems like it would be an easy decision to me…I’m guessing it has something to do with the fact that drinking methyl alcohol (commonly produced along with ethyl alcohol in backyard moonshinin’ stills) causes blindness, but I don’t see how pooping would help with that.

The idea is that if you don’t dump, you’ll eventually “fill up” to the level of your eyeballs.
Am I being “had” by responding to this question?
Oh, well.