Remember too that if a big dog like a German Shepherd or a Rottweiler bites someone, that dog is usually destroyed. If a small dog like a dachshund or a chihuahua bites someone, the person usually just says "ow!" and gets on with life. A lot of people inadvertently allow small dogs to bite or nip because the damage is minor and then the dog learns the habit. Herding dogs, I've noticed, if they have no outlet for the herding instinct, tend to nip the heels of whatever they come across. I know a few people with Blue Heelers. They got these dogs, not because they have acres of land and cattle or sheep, but because they want "a smart dog". These dogs are bred to work and herd and they get nasty without a job. They are not lapdogs or housedogs. Overfed, underexercised.