This may well be the oddest metaphor in a story, but with all the emphasis Saramago has put on human excrement in this book, it bears following it down.
While it is understandable that even in the beginning of our group's incarceration in the mental institution that the toilets would easily become clogged, it didn't hit me as a metaphor until these folk were pooping in the halls and the floors became slick (believe me, my simple statement here is less ghastly than Saramago's details so I won't quote from the book). It was a bit hard to believe that these folks couldn't have found a better way to handle this but they didn't, so that's that.
Even once they are out on the streets the ground is mushy with feces. Blind, okay, but even a pig won't shit where he eats, really, I've raised them. Yet these people, needing badly to go, decide to go right in the garden where an old lady grows some cabbages to eat. That's odd.
Saramago is obviously making a point, and disregarding exactly what the narrator may give as explanation, I do want to remark on a few things. First, and this is what made me think of the Fourth Wall post below, Saramago uses this as a grounding force, this one thing that will happen regardless of what is happening in the world. He also allows the reader to see this, thus not hiding the reality from his audience as is almost always done in drama, movies, plays, tv's, books where it may not be necessary to clarify but there comes a point when the reader/viewer questions the circumstances and wonders how Superman takes a leak with that getup he's wearing.
More though, is the reason to explore why Saramago makes a minor character out of Excrement. For one thing, I find it ironic that the one driving force behind all the actions of the characters is based on their need for food. No emphasis is placed on water, though sex becomes a pawn, and no thought is put into escape. But food is the thing being sought, and the natural and necessary output of food is feces. Does that indicate somehow that maybe food should not exactly be the top priority in these situations? Maybe even death from starvation could be preferable to the loss of soul, i.e., human caring that has come about in this seeking.
The importance of the focus on excrement can also suggest the degradation and depths to which man will succumb eventually if continuing to seek life over spiritual needs. Or it may be simpler: that food follows a known course, in and out, much like man himself.
See, there's more to this shit than it appears…