Why Dogs Bite People

Agression is less common from well-trained, socialized dogs. However, pain, fear, or predatory instincts may cause a dog to bite.

Why Dogs Bite People
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Overview
According to DogsBite.org, a dog bite occurs approximately every 75 seconds in the United States. While it is impossible to know without a doubt when a dog will bite, there are some instances in which the dog is more likely to bite a human. Knowing these instances and planning accordingly can go a long way to minimize the risk of getting bitten.
Pain
Dogs who are in pain will bite people, even familiar people. This is known as pain-elicited aggression, and may occur in a dog who is injured or sick.
Dominance
Some dogs will assert dominance by biting a human who has taken something from it or disturbed it in some way; however, this is unlikely in properly trained and socialized dogs.
Protection of Territory
When a dog feels that its territory is being threatened, it may bite. This instinct is increased when a dog is constantly chained up, which is considered inhumane. The instinct is also exacerbated when dogs are in packs of two or more.
Punishment
Dogs who are struck as punishment are more likely to bite a human than those who are trained using positive reinforcement. Also, dogs who are verbally abused are likely to bite.
Predatory Instincts
In the wild, dogs prey on small animals, which doesn't go away in domesticated breeds. Small, fast moving objects or children will attract the attention--and predatory instincts--of a dog.
Resources
reference
DogsBite.org
reference
DogBiteLaw.com
resource
Dog Bite Statistics