Obvious signs include barking, growling, if the dog's ears are flat or suddenly prick up.

Nearly 5 million dog bites occur in the U. S. each year, according to the American Humane Association.

Ms. Stilwell, chief executive of Atlanta-based Victoria Stilwell Positively Dog Training offers some advice on how to read dog behavior to avoid an attack on a person or other dog.

"It happens when the relative has brought his dog over, or it happens at a friend's house," says Ms. Stilwell."We just let our guard down here."

Says Ms. Stilwell. "Dogs will wag their tails when they are upset or over-aroused."

A dog that attacks is often acting out of fear, says Ms. Stilwell.

Those signs of fear may include a dog yawning, turning its head away when someone approaches, tensing up or staring.

People are usually attacked on private property by a dog they know.

Similarly, if an unfamiliar dog rolls on its back to expose its belly, it doesn't necessarily want to be petted. It might be asking you to move away.

Some dogs salivate when they are stressed, others cower.

Some dogs will slightly lift one front paw in what Ms. Stilwell calls " the anticipatory paw", because it shows that they think something negative is about to happen.

Another subtle warning sign is when a dog slightly lifts its lip to show teeth.

Also, flat tongues are relaxed; curved at the sides means there is tension.

Instead, "take a coat or T-shirt and put it over the dog's head," she says.

"If a dog is on a child and you're pulling it off, you're making the wound on that child deeper, "Ms. Stilwell says.

When dogs can't see, they panic and open their mouths. Thank you.