The cause of animals to bite people is most commonly because the animal felt threatened or was being protective etc.
Most times an animal has to be provoked or feel threatened for the animal to bite someone.
However sometimes an animal may just be naturally aggressive and want to bite people.
Teasing an animal or getting too close to the animal when they don't want you to be so close to them can cause the animal to bite.
Not all animal bites are caused by the animal being provoked but some are.
If you have kids and dogs you need to teach the kids to not tease the animal or provoke it such as pulling on a dogs tail etc.
The dog can react with growling to warn the kid and then the next time it happens the dog could bite the kid.
Never go up and try to touch or pet a strange animal or strange dog because they could bite you.