Coraline, our mongrel, is a nose dog. Compared to other dogs I have known she spends much more time with her nose to the ground and much less with her head up, looking around. I have doubts about her vision; she can see motion readily, but a couple of times she has walked right by deer that were standing very still 50 or 60 yards away. But there is no doubting her nose.
Yesterday afternoon she did again a thing that fascinates me. Walking down our usual trail through the woods, she suddenly stopped and started sniffing. Then she moved to the woods along one side of the trail and began to trot back and forth, nose to the ground. Her excitement steadily increasing, she narrowed the search until she found the trail, then she loped off along it. This took, I would say, 15 or 20 seconds. Once she had found the trail there was no more side-to-side movement, just a straight jog down the scent path. Seeing her coming, the deer sprang from their shelter and ran before her, white tails flashing. (At least, the two deer designated to run from dogs this time sprang up and ran.) Coraline accelerated to pursuit speed and disappeared into the forest, returning five minutes later flecked with foam.
She lives in a different world than I do, a world full of identifiable smells and crisscrossed by the trails of animals and people. She knows when deer are near without ever seeing them; you can see her shift into alert mode, full of energy and sniffing all around. Often she does not find a trail, and so she only sniffs, but when we do cross a trail she always follows it. Sometimes she gives up quickly, I suppose because she has decided the trail is too old to bother with. When it is not, she becomes a hunter.