We can't smell sh@t. Not like most mammals.
We just aren't able to discern the dozens of details that are there for the well-developed nose to know. The who, what, when and why of each scent. To, basically, be able to sniff back into the recent history of wherever you are, and know what came and went before you.
Here are two series from a set in the Santa Cruz Mountains that show this ability in spades.
The first five are of a cutey bobcat that was caught early one morning while spraying a rock, and then showed its fear of the camera by doing some cheek rubs on it. Yet another behavior that bobs, house kitties, and even cougars do to lay down and pickup scents.
3 days and 4 hours later, this nubby buck came poking along the trail.
Notice the spot he sniffs and how he reacts...
- Wikipedia - Spraying (scent marking)