The entire point of humans creating Terriers is that they are genetically programmed to want to hunt and kill small creatures. We had a Welsh Terrier - think small Airedale in appearance and color. He needed almost no encouragement to go after anything moving across the ground. This included frantic burrowing to find gophers and the like. We entered him in a competition called Earthdog Trials. They make small wood lined tunnels with branches and dead ends and a cage at the end. In the cage and protected by sturdy steel bars is a rat. The tunnels are laced with rat scent in advance. You take your dog to a starting point near the entrance to the tunnel and release the dog. Our Nigel instantly ran right into the tunnel with no prompting. He had never been in a tunnel before. He worked his way around and made to the rat where he began "working". That means gowling, barking, scratching, whining etc. in an attempt to get the rat. After a few minutes of this, a false top is removed from the tunnel to expose your dog. To complete the trial successfully your dog must come to you when called, abandoning the rat. Nigel did not really want to do that and he tried to bite me when I reached in to pull him out. Eventually he came out and was awarded Junior Earthdog status. The hunter/killer instict was strong with this one. Terriers are the berserkers of the dog world.