Aside from some Nordic and Spitz breeds, most dogs are not capable of verbally saying NO (okay so they don’t really say “no” but they can Arooo in a way that sounds like it)!  They use their own physical language and rely on us to understand it–or at the very least have a rough working understanding.  They also rely on their handlers to advocate for them–if your dog looks uncomfortable don’t let people approach and pet.
Unfortunately there are way too many dog owners who have very little working knowledge of dog body language and cannot effectively advocate for their dog.  This lack of awareness of canine body language absolutely leads to dog to human bites and even fights between dogs.  It really is of the utmost importance to educate ourselves and other dog handlers how to read some of the most basic canine “phrases.”
I’m going to post and give a little blurb about a variety of photos that show how dogs “say no” both to humans and to other dogs.  Learning to recognize these postures/actions can help you prevent a dog bite.  Look at the photo before reading the analysis and ask yourself, is this a dog you would pet if the pet owner said “sure,  you can pet him.”
Dogs do NOT like hugs!
Heidi is being embraced by an adult female and is clearly stressed out.  How do I know?  Heidi is yawning, her ears are back and to the side (or they are mid flick), and she’s leaning away from the embrace.  She is also mid blink and an increase rate of blinking is a sign of stress (can’t tell the rate of blinking from the image though).
*
GET BACK!
Willie is sending very clear, get back signals. He has a very hard eyes, intense stare, has some whale eye it looks like (hard to tell w/ the blue), his ears are quite forward, his whiskers are forward, has an aggressive tooth display, his body is cocked back ready to strike, and his tail looks to be flagging (a staccato-like wagging motion).
*
I’m not comfortable!
Neither girl is particularly comfortable in this photo.  Risa is offering quite a few appeasement gestures: low head, curved approach, and I think she licked Shayne’s muzzle.  Shayne responded by dropping her head, licking her lips, looking away and giving a whale eye (barely visible in photo).
*
I do not like this!
This pup is being hovered over by a handler while having his collar grabbed.  His ears are pulled back, he’s crouched a little low, he is licking his lips, and his weight is shifted backwards (just waiting to flee).
His tail is wagging…but does he look happy?
*
Not okay, please go away!
Risa is very uncomfortable here.  Her ears are pinned back, she has a huge whale eye, her commissures are pulled forward, and her brow is furrowed slightly.  She may also be about to roll on her side, which is a cut off behavior (remember Shayne’s belly photo from yesterday?).
*
Can I run away yet?
Chloe, is very uncomfortable and given the chance, would probably flee in an instant.
Chloe’s ears are back and to the side, her mouth is tightly closed, her brow is furrowed, her tail is very low (shadow indicates), she’s walking a little “low” and her weight is backwards. If she was stationary, the raised paw also indicates concern.

*
I’d rather you didn’t pet me…
She is doing a very strong look away, her ears are pinned back, mouth closed tightly, face is tense, and whiskers are pushed forward.
This is the look that many dogs give when they don’t want pet, yet handler and stranger have no clue what the dog is saying.  For a dog with a low bite threshold, this could be all the warning you get before a bite happens.
*
I’m pretty uncomfortable…
This dog is not smiling and relaxed.  He is showing multiple signs of being quite stressed and if it were the “wrong” dog, it could be enough of a warning to bite.
His ears are pinned back, he is avoiding eye contact,  has moved as far away from the camera as possible, his eyes are dilated, his face is tense, and he’s panting (unsure of whether that is weather related).

*
UH OH!
Okay, aside from the photobomb by Tas, this picture makes me so uncomfortable!

Not that you can tell, but what’s going on in this photograph is both slow/no movement and then a momentary freeze by Shayne.  Both very ominous signs of bad news.  Risa (the darker dog) is offering some calming signals along with some stress signals (she’s a little confused), her ears are pinned back, her head is lowered and curved (calming) but her whiskers are pushed forward, her mouth is tightly closed, and she is staring (yet looking away).  Shayne is not doing a good job at communicating. She is very stiff, ears forward, mouth tightly closed, yet her weight is backwards.  These two girls got in quite the pickle in this interaction… they got too close and neither felt comfortable enough to know how to get out of it (though part of Risa was trying to make Shayne comfy… yet the other part wasn’t LOL).  As soon as I saw the stillness, I called Shayne away because a scuffle would have happened if someone didn’t break the tension–again just looking at this photo I can feel the tension.
How many of these dogs would you have approached if the owner said “SURE!” ?  All of these dogs are giving signs/warnings that they are uncomfortable.  While some or more subtle than others, all are communicating stress/discomfort.  For some dogs, these are the types of warnings that are given before a bite (though I would venture that most dogs will give more warning than the subtle ones here).  Not all dogs will growl loudly or give an impressive aggressive tooth display… many will give a whale eye, yawn, lip lick, blink and look away before they choose to go in for a bite if the person continues to get close/pet (a bite is often a more physical communication that they want you to back off).
So, what does this mean?  Dogs who bite don’t always look aggressive to the naked eye but they all will give you some signals.  So before you pet a dog or allow someone to pet your dog, ask your dog–what is he/she saying through their body?  Are they comfortable?  Do they want to engage? Or, do they want to get the heck out of Dodge?  Even if a person says you can pet their dog, if the dog is giving off uncomfortable/fearful/anxious type body language, take the safe route and admire from afar.
Photos are still captures, it’s very hard to catch some of the warning behaviors like slow or little movement, paw raises, pacing, freezes, dogs who aren’t eating, and hyper vigilant behavior.  Also there is a stress behavior that is actually pretty common that I couldn’t find a photo of (for good reason) .  Dogs who are stressed will often break the tension by sniffing or licking their genitals or butt.  Shayne does this with her tail, if she’s stressed, she’ll plop down and nibble the base of her tail.
Thank you to Crystal and Jamie for the use of their fantastic photos!!
**Just an aside, photos caption just one instance in time, these photos may not represent the actual nature or behavior of the dog… it just captures about 1/120th of a second in time and in that 1/120th of a second the dog was displaying those behaviors.