I came across this video online and wanted to repost it because most dogs that are found in this state like Janie here do not get a second chance: http://www.dailymail.co.uk/news/article-2319054/Road-recovery-The-heartwarming-video-puppy-wouldnt-let-near-learning-trust-humans-again.html
The back story is that Janie was hit by a car and broke her back. The Bill foundation paid for Janie’s surgery and naturally she was scared of human beings given how much pain she had been through. If you open the video on this page you will notice her snarling and in a state such that no volunteers could come near her.
When dogs are in shelters in this state, it is usually game over. They are termed vicious, dangerous, or whatever which then ultimately leads to euthanasia. There are so many dogs with no behavior problems euthanized that it is very unlikely that a snapping dog will ever be adopted.
This video of Janie and a volunteer is particularly heartwarming because most dogs can be rehabilitated to a state where they would be great family dog. Dogs are born nice but humans do a lot to them that can create their fear issues and altered temperament. Of course, there are some animals born that are wired in the wrong way but that is an extremely small fraction of a percent of dogs. As we continue to fix the dog/cat shelter/adoption system in this country such that we become a no-kill country I expect that ultimately we will make our way to spending extra time on dogs with fear issues. Many great dogs like Janie are euthanized needlessly so if you see a dog with issues that you are thinking about adopting, get the help of an experienced dog trainer and give her or him a chance.