Picture the scene: you're walking along the road with your dog when - horror of horrors - another person with a dog appears at the end of the street. You start to breathe faster, your heart rate speeds up, you clutch the lead tightly to you, keeping your dog's head close. Your dog spots the other dog, and lunges forward on the lead, barking ferociously. You gasp out broken commands as you try to keep your feet on the pavement. The other person...