I was grouse hunting in Washington state, for spruce grouse, which was usually a futile effort, but the season opened for grouse before the other upland birds opened. Out strolling through the woods, dog started circling and sniffing around the base of a big spruce tree, didn't see any birds, no points so I thought he was probably sniffing some varmint. Finally got him out of there, walk away abut 30 yards and hear that loud noise game birds make when they are flying and watch a couple of grouse fly out of the top of that tree.
Another time a group of us were walking across a recently mowed hayfield to get to another spot, my dog locked on a small clump of dried grass, I walked over there thinking, yeah right - got about a foot away and a hen pheasant jumped out of there, I was looking right at her and never saw her.
I learned to trust that dog. Sometimes he'd give you a false point, but if he got locked on something there was a good chance there was a bird there.