Why Do Dogs Smell Each Other's Butts?

This video explains why dogs smell each others butts.  It's to do with chemicals that some gland secretes in their anus.  The dogs are able to get a big range of information about the dog they are smelling.

Wonder if humans interact in this way at all, through smell I mean or what other ways we have to communicate.  Anway found this video interesting so posting it.

Darcy Lee