Dog bites can be prevented by learning the body language signals that dogs give off in the lead up to a bite. Dogs generally don't "bite out of nowhere" unless these early signals have been ignored repeatedly or punished.
Here are the signals that a dog will give as they move down the road to a bite, and what they mean:
1) Displacement Signals - "I'll act distracted to take the pressure off"- Sniffing- Scratching- Goofing around
2) Calming Signals - "I'd really like things to calm down"- Licking lips- Yawning (often with a squeaking noise)- Turning head away or moving away- Moving in slow motion
3) Stress Signals - "I'm really getting scared now"- Heavy panting- Sweaty paws- Trembling- Big wide eyes (called whale eye or half moon eye)- Hackles up
4) Preparing for Action / Assessment - "They're not stopping, maybe I'll have to defend myself"- Stiff, frozen posture (conserving energy)- Staring wide-eyed without blinking (hard stare)- Mouth closed
5) Last Warnings - "Please stop and go away, this is your last warning"- Snarling or lifting lip up vertically- Growling- Snapping the air- Punching with nose (muzzle punch)
6) Attack - "This is the only way to keep myself safe"- Lunge- Bite
The earlier you take an exit, the better your chances will be of avoiding a bite! The rule of thumb if you're not sure what to when you think your dog might be heading down the road to a bite is ADD SOME DISTANCE between your dog and whatever is upsetting them.