"Track!" said my master. Like any good tracker-dog who has received the command  he most loves, I gave a bark of excitement, put my nose down to the ground and sniffed. The ground was rich with smells. Even in the high-class housing area where we were working, the stones held traces of many sole and confusing scents (smells). As I searched for the scent that would give me a clue to the tail of the guilty man, my tail wagged slowly, thoughtfully, delightedly. Work was like play to me; I enjoyed it. A small group of people gathered behind us. Among these onlookers was the old caretaker of the building next door to ours. He spoke in a scornful voice, "You actually think your dog might catch a thief three days after the event?" My master said nothing, but I'm sure he must have smiled. I did not turn to look. I knew he would not speak unless it was to give me a new command. I needed to concentrate. My task was difficult. I had to pick out one scent among the many that lay about and then tracked it to its source. "You're wasting your time," said the caretaker. I looked at him without raising my head. He was running his hand over his fat stomach. His rough palm and smooth shirt combined to make a slight noise. It was part of my training to be aware--often it is only a little whisper of a noise that alerts you to be drawing of a weapon. But of course the aging caretaker was going to do no such thing. There was no smell of fear or nervousness about him. He was merely being clever and talkative. "I've seen many tracker-dogs in my time," said the caretaker to the onlookers. I served with the police years ago. We would never have thought of using a tracker-dog to find a car thief. Impossible. Everyone knows that dogs are useless in such matters. In a sense he was right. I'm sure there's no need to tell you that, just as a dog's hearing is much better than a human being's, so his sense of smell tells one thing from another far better than a great detective. If Sherlock Holmes could work out that a man had had an egg for breakfast by seeing the yellow stain on his mouth, a trained dog could tell you whether the hen that laid the egg was healthy or not. I know it sounds funny and I mean it to be. But I'm not exaggerating. A dog can tell you--if you understand a dog's way of communicating--all this and more without even setting eyes on the man he is investigating. In the dog's opinion, its sense of smell   _  .
can give us fewer details about what a human has already discovered can achieve more than what a human's only if the smell is not hidden is particularly trained to pick out one scent among hundreds is better than its sense of hearing when it does tracking