Not all pit bulls are bred to fight. Conversely, German shepherds, dobermans, rottweilers, mastiffs and other terriers display "gameness": the tendency to attack.
The term pit bull is often used loosely to describe dogs with similar physical characteristics, and the morphological (physical) variation amongst "bully breed" dogs makes it difficult for anyone, even experts, to visually identify them as distinct from "non-pit bulls".
Pit bulls in particular display a tenacity in fighting and will carry on attacking even if they have broken limbs and are bleeding. So how should you react to one?
- Stay where you are
If you think a dog is about to attack, don't run. Predators are hardwired to chase if their "prey drive" is triggered. Even Usain Bolt couldn't outrun a dog
- Show no signs of fear
Stand still. If you can, climb up or on to something high, such as a tree. Dogs can jump - some pit bulls can hop up as far as two metres - but they can't climb.
- Protect larger arteries and veins
If you've got something to hand, such as an umbrella, extend it to give the dog something to attack. Try to stop the bite from going near your legs, face and neck.
- Don't attempt to pull your arm out
When pit bulls attack, they cause damage to their prey with what's called the "bite, hold and shake". Try forcing your hand down into its throat to make it choke.
- Try not to panic
Once the pit bull has got its teeth into your arm, it won't let go (illegal pit-bull trainers use "breaking sticks" to lever the jaws open). Stay upright as long as possible and, if you can, try to restrain the dog by putting your free arm around its neck.
- Hold out for the cavalry
Either wait for help to arrive or try incapacitating the dog: suffocation is a possibility, and the eye sockets are particularly vulnerable.
A nine-year-old boy in the US recently disabled a pit bull by holding the dog in a Brazilian jiu-jitsu "reverse naked choke" hold.
If the police arrive before you bleed to death, they will exterminate the dog. Good luck.