Old Argos

Why is it that the death of an animal in literature or on the screen will kick you in the gut in a way that no human's death is likely to?

Now, as they talked on, a dog that lay there
lifted up his muzzle, pricked his ears. . .
It was Argos, long-enduring Odysseus' dog
he trained as a puppy once, but little joy he got
since all to soon he shipped to sacred Troy.
In the old days young hunters loved to set him
coursing after the wild goats and deer and hares.
But now with his master gone he lay there, castaway,
on piles of dung from mules and cattle, heaps collecting
out before the gates till Odysseus' serving-men
could cart it off to manure the king's estates.
Infested with ticks, half-dead from neglect,
here lay the hound, old Argos.
But the moment he sensed Odysseus standing by
he thumped his tail, nuzzling low, and his ears dropped,
though he had no strength to drag himself an inch
toward his master. Odysseus glanced to the side
and flicked away a tear, hiding it from Eumaeus,
diverting his friend in a hasty, offhand way:
"Strange, Eumaeus, look, a dog like this,
lying here on a dung-hill. . .
what handsome lines! But I can't say for sure if he had the running speed to match his looks
or he was only the sort that gentry spoil at table,
show-dogs masters pamper for their points."

You told the stranger, Eumaeus, loyal swineherd,
"Here—it's all too true—here's the dog of a man
who died in foreign parts. But if he had now
the form and flair he had in his glory days—
as Odysseus left him, sailing off to Troy—
you'd be amazed to see such speed, such strength.
No quarry he chased in the deepest, darkest woods
could ever slip this hound. A champion tracker too!
Ah, but he's run out of luck now, poor fellow. . .
his master's dead and gone, so far from home,
and the heartless women tend him not at all. . . .

But the dark shadow of death closed down on Argos' eyes
the instant he saw Odysseus, twenty years away.