High in the mountains of North Wales in a place called Llanymawddwy, lives a shepherd named John Jones with his wife Mari and his black and white dog Mack. I stood one misty summer morning in the window of their farmhouse watching John on horseback herding the sheep with Mack. A few cows were quietly chewing their cud in a nearby corner while perhaps a hundred sheep moved across the dewy meadow toward the pens where they were to be dipped. Mack, a champion Scottish collie, was in his glory. He came from a long line of working dogs, and he had sheep in his blood. This was what he was made for, this was what he had been trained to do. And it was a marvelous thing to see him circling to the right, circling to the left, barking, crouching, racing along, herding a stray sheep here, nipping at a stubborn one there, his eyes always glued to the sheep, his ears listening for the tiny metal whistle from his master, which I couldn't hear.

Mari took me to the pens to watch what John had to do there. When all the animals had been shut inside the gates, Mack tore around the outside of the pens and took up his position at the dipping trough, frantic with expectation, waiting for the chance to leap into action again. One by one John seized the rams by their curled horns and flung them into the antiseptic. They would struggle to climb out the side, and Mack would snarl and snap at their faces to force them back in. Just as they were about to climb up the ramp at the far end, John caught them by the horns with a wooden implement, spun them around, and held them ears, eyes, and nose submerged for a few seconds . . . .

When the rams had been dipped, John rode out again on his horse to herd the ewes which were in a different pasture. Again I watched with Mari as John and Mack went to work, the one in charge, the other obedient. Sometimes, tearing at top speed around the flock, Mack would jam on four-wheeled brakes, his eyes blazing but still on the sheep, his body tense and quivering, but obedient to the command to stop. What the shepherd saw the dog could not see the weak ewe that lagged behind, the one caught in a bush, the danger that lay ahead for the flock.

"Do the sheep have any idea what's happening?" I asked Mari.

"Not a clue!" she said.

"And how about Mack?" I'll never forget Mari's answer.

"The dog doesn't understand the pattern only obedience."