Sierra Spaulding, I’m taking it from here:
On smelly things: the evolutionary account I’ve seen is, to transmit smells of interest back to the den, to keep the other canines informed. All interpretations of dogs as wolves in dens, of course, you should read with caution. And the answers to Why do dogs sniff the grass and suddenly start rolling their bodies over it? have a rather different take.
Like Shannon Gilles said: to submit, and thence to ask for belly rubs. When Jenny the annoying lab–kelpie mix with abandonment issues switches from exposing her belly
to wiggling insistently (as if she’s found some delectable animal corpse, only she’s on porcelain tiles in Schloss Nicholas, which were laid down before I inherited a canine), and sticking out her dodgy leg, then we believe she is demanding not so much a belly rub, as a leg rub.
Yes, the fricking dog gets leg rubs. Why do you ask?