Dog's can't talk, howl and bark yes but talk no.
So they can only speak to us through their body language. Sadly many people cannot read a dog's body language.
Which can make teaching and understanding your dog's behavior extremely difficult.

Step 1: Content, Happy, Interested

We usually know these signs, but for those who don't here you go
(Order of Pictures)
Happy:
Ears are relaxed or up and the dog's tail maybe wagging. Most dogs whom are happy will be panting, some not. Dogs maybe concentrated on a toy or treat.

Content:
Very similar to happy. Ears are relaxed, dog's muscles are relaxed. Dog is usually laying down or sitting.

Interested:
Ears are erect, eyes are wide, muscles are tense.

Step 2: Fear

Fear is often missed by some people. But for others it sticks out.

Dog is tense. Avoiding eye contact, ears are flattened to head. May be hiding in a corner or is lying down and is keeping to themselves. Dog is cowering, tail between legs. Head is lowered and eyes are wide or closed. Dog may be panicking running around and barking, depends on the dog.

ANY SCARED DOG MAY BITE OUT OF FEAR!

Step 3: Dangerous Signs

This covers the signs that can lead to a bite.
Not all dogs are the same so sometimes the warning are different for different dogs.

1. The first thing you have to take into account is the situation. If the dog is stressed or is in a tight situation do NOT put a hand or your face next to a dog's mouth. If the dog is not yours and you have permission by the owner allow the dog to sniff your hand and wait until the dog has finished sniffing it to touch him. ALWAYS PUT YOUR HAND UNDER THE DOG'S CHIN when you are allowing him to sniff. Over the head = dominance.

2. If the dog cowers, don't touch him. Cowering is a sign of fear, fear is a sign of stress.
3. Ears, if they are back it's not OK to touch him.
4. Averting eyes. A dog will acknowledge you by looking you in the eyes. This is a sign of respect, he sees you as an equal. If he doesn't hold eye contact he is not interested and it's not a good idea to touch him.
5. Teeth, everyone knows if a dog shows you his teeth don't touch him. EVER! It is completely dangerous! But if you choose you to teach a dog a lesson and move towards him; YOU WILL BE BITTEN! A dog will accept a challenge, especially if a stranger is challenging him.

ANY DOG THAT BITES A PERSON WILL BE PUT DOWN!

To set one thing straight there are no dogs the have EVER been made to attack a person without training. And in the case of the reporter Kyle Dyers she missed several signs of body language the dog tried to express.

http://www.youtube.com/watch?v=Q7HoL2VqvYg the "attack"

Step 4: Questions?

I didn't go over a lot of the signs and some dogs have odd situations where they will act a certain way only in a certain situation.

I adopt dogs and rescue them.
I enjoy teaching dogs and learning more about them everyday!