It’s a running joke that, according to Victor Hugo, Paris has the best of everything. And while Paris has the worst, most horrific sewers (up to this point), Hugo actually goes so far as to say that Paris has the best sewage. As he complains about how we flush all that fertilizer out to sea, he actually describes “Parisian guano” as “the richest of all.”
I can’t help feeling this extended description of what it’s like to sink into quicksand is a metaphor…
Incidentally, Wikipedia suggests that if you don’t flail about, you’re unlikely to sink completely in quicksand because it’s denser than the human body. Of course it can trap you long enough to dehydrate, get caught by the tide, eaten by wolves, etc. Though Hugo points out that in the sink holes of the sewers, density varies wildly.
“The man folded his arms and gave the grating a look of reproach. A look proving insufficient, he tried giving it a push.”
— Javert vs. the sewer grate.
Cataloguing Marius’ injuries: Except for a broken collarbone, they’re mostly shallow – there’s just a lot of them. His lengthy convalescence and fever are probably due to infection. Hazards of the sewer as an escape route.