WHAT ON EARTH can he be thinking? His tail moves slowly across the boards of the floor a little like a rudder someone's testing; brown dog eyes gaze up and then away to some vague object of dog interest. What on earth can this black dog be thinking?

He is a Labrador, 4 years old, very large bones. Jaws very strong, coat very good except one place on the left ear that got torn, just slightly, early in the winter and won't heal, though everything has been tried on it, right down to chapstick. His name is Shark, because of the jaws.

He is a hunting dog and very good at his job. Qualify that - he is like the racer who occasionally has runs of brilliance that stun his opposition, yet most of the time makes mistakes that keep him from victory. It's during his hunting time that I think most about him, and find myself talking to him a lot, which leads me to wonder. . . What on earth CAN he be thinking?

The answer, I have decided, is NOTHING. plain dark dusk nothing, silent mist blank nothing. The great visionary drunkard and water Malcolm Lowry, who in his delerium tremens often saw dogs, described them in an unforgettable way, writing of a dog he saw in bar in Mexico. "Beady, gentle eyes . . . these animals, these people without ideas."

This melancholy phrase, like a bad movie review, bring up a whole plague of thoughts, the main one being that ever since I can remember I have made the same mistake, which is to confuse intelligence with worth. Smart equals good, dumb equals bad. Like marshmallow fluff, this standard gets applied to everything, because we are always thinking and seldom doing, and I can well remember trying to force the black dog past this intangible mark, before I knew him better.

"How damned intelligent this creature looks," I would muse, "how his eyes gleam with knowledge."

For he does look intelligent and handsome, too - we insist on our beauties being intelligent and are disappointed when they are not.

Other Labrador owners have practically humanized their dogs, assigning them moods, whims, whole chains of reasoning, smiles, grimaces, Snoopy, the apothosis of dogs, is smarter than Charlie Brown. Truth is even stranger than comic strips, for I have heard people talk about their dogs as if the dogs were about to write letters.

The subject of this examination is before me now. A week ago he got into the worst dogfight of his life and was almost killed by a German Shepherd that felt a certain female in heat was his property. These are the facts of dog life. As a result, Shark hops aroundon two sore legs, trying to balance on the two good ones, his broad and totally black chest covered with deep cuts, looking like a dejected lover.

Otherwise, he is a nice piece of flesh. Terrific coat, teeth that shine, large round feet like balls, and brown eyes surrounded by white so white - the only white as white as fresh enamel on wood paneling, and the paneling must be owned by some very very rich.

But one just can't quickly skip over his mentality as if it were some pleasant subject after a good lunch; because there is something, perhaps a group of nerve endings encased in library paste, behind those eye. It is something that has led to some curious events and days and has led also to the conclusion that intelligence is not necessary, at all, for one to make his mark on the world.

Shark was well educated by private tutors before approaching his vocation as a retriever and without exception his instructors noted his strength and willingness, but fell silent on the subject of actual skill. I soon took him to the field to test his mettle.

It was a day in December at a fashionable farm in Virginia, moist and cloudy and cold enough that quail could set and fly, the habit of one owner, however, was not to use pointing dogs, but to rely on his Labrador duck-hunting dogs to range in front of the gums and then retrieve the fallen birds. Everyone was dressed in his best hunting gear and the host wore an impeccable tweed hat that could well have graced a marquis or duke - it was the kind of event that makes me fear, more than anything, being the conspicious fool. Everyone was expecting a mighty slaughter of game and a roaring fire after.

The dogs shot off, sleek and black, so complete against dead straw and clay that they looked every second like those color slides that are better than seeing real. They rushed eagerly and purposefully in front of the line, and Shark among them, Shark by no means the least among them. Halfway across a field a covery flew and powder puffed from two guns, two birds fell, one a mere 20 yards from where I walked.

Knowing Shark's high marks for eagerness and rushing into the fray, I dashed to the place where I had seen the bird lie trying to get there before he did. Unfortunately, though I had marked the bird with all the care I could, I could not find it immediately and the black dog, running nose down, began to cover the area. With a primal grunt he seized the bird. Before I had time to look around for congratulatory glances, I noticed that the equal had disappeared, and thinking he had droped it, as retrievers sometimes do short of the final destination, I walked over, trying to look the casual and grand quail shot. Something in his face and motions looked queer and with a sudden jolt of horror I realized that he had swallowed the bird and only half a foot, claws looking like shiny twigs, stuck out of the corner of his black lips.

I threw my gun down and jumped on him, grabbing his jaws and pulling them apart with all my strength.

Though he grunted when I knocked him from his feet, he would not let go. I sat on him. I put my knees on him while trying to encircle his throat to keep the bird (what a dreadful passage from this world it must have known) from going down his gullet. He would not let go. Finally I picked him up in an Adrenalin blast, held him over my head and threw him down as hard as I could. The result was nothing plain awful nothing. He swallowed, he shook himself, he looked up with a look that expressed - nothing at all.

The host, aghast and staring said, "My God . . . My God . . . He ate it all."

That was the end of the incident, but only the beginning of my notoriety and a great number of frankly graceless jokes about what would be eaten next.

He never ate another quail, nor has he eaten a duck, nor has any sign of the original eaten quail ever surfaced - his powerful stomach must have atomized it.

Since the incident he seems to have learned some rudiments of the breed. In fact, simply because of his animal energy and eagerness (almost madness, the way he dances across the moonlit lawn in the dark before duck hunts), he has become very good at hunting. He will crash through ice, which some retrievers find hard, he will press through flooded willow thickest, and he will return again and again to be chewed up by the German Shepherd, though he is no fighter, and to my knowledge, no lover either.

Nor can he adapt himself very well to domestic arrangements of the city. He gets lost near the house and cheerfully turns up in someone else'e yard (one of these finders told me how intelligent he seemed). But after warning everyone innumerable times about closing the back gate, I leave these wanderings in the hands of fate. He also cannot learn to keep his tail out of the jaws of a rocking chair's rockers.

But he loves gunpowder and he loves excitement and he loves eating; which I'm forced to say, is a state of equilibrium better than my own, and in the words of the famous hunting toast, raised with glasses of rich port over cold floors, with the smell of dog fur, leather, oil and smoke: "A consumation devoutly to be wished."