How does Charles Johnson use imagery in Menagerie, a Child's Fable?

Imagery:

"A pious German shepherd (Black Forest origins, probably) with big shoulders, black gums, and weighing more than some men, he sat guard inside the glass door of Tilford's Pet Shoppe, watching the pedestrians scurry along First Avenue, wondering at the derelicts who slept ever so often inside the foyer at night, and sometimes he nodded when things were quiet in the cages behind him,
lulled by the bubbling of the fish-tanks, dreaming of an especially fine meal he'd once had, or the little female poodle, a real flirt, owned by the aerobic dance teacher (who was no saint herself ) a few doors down the street; but Berkeley was, for all his woolgathering, never asleep at the switch. He took his work seriously."

Throughout this turmoil, the shouting, beating of wings, which blew feathers everywhere like confetti, and an angry slapping of fins that splashed water to the floor, Monkey simply sat quietly, taking it all in, stroking his chin as a scholar might.