Dogs' sense of smell?

PROEMIUM:

If you have a weak stomach or just don't like "gross stuff," don't read this inscitia. Honestly, writing about it is a pretty unpleasant task for me, but I feel obliged to "air it out" (!) here, if anywhere. Scientia inscitiam vincere debet!

INSICITIA:

Why do dogs not find human farts unpleasant? Similarly, why do they not mind sniffing the toilet and other animals' urine and feces (in some cases even licking them!)? Do dogs think anything smells bad?

COGITATIO:

These phenomena truly baffle me. I can't possibly believe humans' sense of smell is better than most dogs'. I'm also not willing to say humans' unhappy reactions to farts are purely socialized (whereas pain tolerance is largely conditioned).

My first hunch is that somehow humans tap more directly into a certain section of the so-called olfactory spectrum. I imagine dogs react just as unfavorably as we do to the smell of rotting flesh, but perhaps that is because "the maggot smell" belongs in a more biologically universal section of the olfactory spectrum. We can smell the stink of farts more sensitively than they can; note, indeed, that while we find dog farts stinky, they don't find their own or our farts stinky.

A second hunch is that, paradoxically, because dogs' sense of smell is so much keener, they can smell 'beneath' the stink and try to get a sense of what produced the fart (i.e., they are smelling the remnants of our food). Sort of like how we hone in on the scent of raisins as we at mediocre raisin bread. We can smell both, but we attune our nose to one smell in preference to another. In the case of farts, however, our olfactory powers are too feeble to break through the obvious outer fart-layer to access the remnant food smells.

RESPONSUM:

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