The currency of a human and a dog is play.

At first, the human and the dog size up one another.  Who is this strange beast?  Are her intentions noble?  Does she mean to steal my squeaky toy?

The dog smells the human; he is unknown.  The human talks to the dog; the dog cocks her head but fails to understand.  They are unintelligible. 

But the dog knows common grounds.  She picks up a squeaky toy, and with butt sailing high and tail wagging wide, she taunts the human as a fiend invader of her territory.

He cocks his head but fails to understand.  She is ferocious and simultaneously goofy.  He jumps forward with one bombastic step.

She leaps for joy.  The human has understood.  She runs a tight circle around him, tail flailing.  No matter what ~ and everything depends upon this fact ~ he must not get the toy.

They negotiate the rules of the game.  It involves the chase.  And it involves an epic tug of war.  Practicing the "drop" command during the game is forboden and cheating in her eyes.  But she will do it for a treat.  

The currency of a human and a dog is play.  It is where we bond.  It is when we learn to trust.  It is how we learn to communicate.  It is when we learn to love.