One recurring example of symbolism is the black lab, and Crozier even gives explicit clues to the meaning of the dog.

A black Lab

lopes up the path, doubles back.

All energy and muscle

and too much love, he bumps our legs.

He belongs here, the family pet.

The dog begins as just a dog, a family pet that of course fits in the scene with the mother and daughter walking.  As the poem continues, he changes:

This morning he has more to do

with time, how it runs ahead and keeps

returning, our smell on its muzzle

along its back. I'm afraid

he'll knock my mother over.

Crozier suggests that the dog itself symbolizes time, how it can run back and forth and in some ways be annoying with its constant presence and can even be damaging and a little bit scary.