It is amazing just how 'locked on' dogs can become.
I watched Karl sneak up on a blade of grass that was moving, for about twenty minutes... Finally, I got tired of watching and brought him reluctantly into the house. It was dark and getting cold enough to end the game.
Sometimes I just have to physically turn his head before he'll move, once he's locked on to something.
The other day I went outside to find Karl had dug up a vole. He was laying there, panting beside his quarry. As he watched wagging his tail, the little vole lay there kicking his tiny legs. I can't say I was really sad for the vole. There's plenty tearing up my yard, to not miss a few.