Why does my dog sniff other dog's butts, or eat grass? (whydoesmydog.com)
But after getting zapped with mild electrical shocks when exposed to one molecule but not when sniffing the other, volunteers rapidly learned to easily tell them apart. (scientificamerican.com)
Every dog's secretion has a different odor to identify him, which is one of reasons why dogs sniff each other in the rear when they meet. (raisingspot.com)