It's wrong to sniff your dog's poop.
Leon notices there is some blood in his dog's stool.
Leon wants to figure out what's wrong with it.
Leon bags the poop on the way back to the house to take to the vet.
Leon bends down to take a whiff to see if he can smell sickness.
The vet looks at it, examines Leon's dog and manages to diagnose and cure it.
Leon slips landing face first right into it, getting it all over.