Dog owners are very used to this question, commonly asked by people who want to pet, but perhaps aren't used to dogs or have maybe had bad interactions with dogs in their past. Usually most pet owners will respond with a "No, he's very friendly!" However, the truth of the matter is that any dog will bite if they feel they have no choice to defend themselves.
I read a recent news story out of Connecticut about a horse that bit a child. A mid-level Appellate Court has ruled that the horse belongs to "a species naturally inclined to do mischief or be vicious". This ruling came as a result of the owner's testimony that while he didn't know of any prior situation where the horse had ever bitten anyone, "Scuppy was no different than other horses that would bite if a finger was put in front of him".
The ruling saddens me for many reasons. First of all, it shows a severe lack of education in animal behavior. Animals are not people, and should not be expected to behave as such. When I'm asked by children in HAWS education programs if an animal bites, I've sometimes said "Anything with teeth CAN bite", and then I'll go on to explain that if the animal feels threatened, or if the interactions are inappropriate an animal can bite. That's why it's very important to understand an animal's natural behavior and show respect in your interactions.
Secondly, if the standard of determining if a species is vicious is that they have a tendency to bite if presented with a finger, we have many other species that can be added to that list. Guinea pigs, rabbits, hamsters and rats will many times bite if a finger is placed in front of their faces.
The bite by this particular horse sounds as though it was serious (the child was bit on the cheek and tissue was removed), however this type of bite is a very rare occurrence between equines and people. If we start to move towards zero tolerance of animal to human injury, our society will be left without being able to have pets of any kind. And if we used that same standard towards ourselves, we ourselves would be deemed a vicious species.