Triggers for Dog Aggression
It's hard to understand why your dog can suddenly become hostile, especially if he has always been friendly. His anger may be directed at his owner, strange people or other things.
Below are some of the most common triggers:
Being picked up
The same goes for various veterinary examinations and procedures, including but not limited to:
Eye exams
Dental examinations
Ear examinations
Injections of any sort
Medication delivery
Being restrained for examination
Being on the examination table
Being pet or touched
Go to http://www.dogster.com/dog-training/dog-aggression to read more about these behaviors.