The Look on the Dog's Face

How is it dogs know already
the big circling game they play with boys,
where the kid and the dog both get down
with forearms along the ground like sphinxes?

Then the boy runs at the dog,
and the dog takes off in a circle
that brings it back close enough
to be touched but not grabbed,
and changes tack to make a figure-eight
out the other side with the boy
in the hour-glass door.

The game needs a lot of space to do right,
a field, or a biggish backyard,
though I have seen it done on a steep hillside.

The look on the dog's face
is a tricky and barely embodiable joy.