Recently we had an impromptu fire drill while working with a future therapy pup in a High School. This gave us a learning opportunity and in addition it got our team caught in the hallway during class change. I had the camera rolling and the pup exhibited a plethora of subtle behaviors that are associated with being nervous or scared. This pup exhibited a large panting "grin", inconsistent tail wagging, hypervigilance, fidgeting, and whale eyeing.
Every dog exhibits nervousness and fear in slightly different ways. It is important to learn how your pup reacts in fearful situations. These signs can warn us when an animal is approaching an emotional threshold. Knowing this will help families avoid dog bites and creating anxiety issues in the future.
This is a fantastic infographic for Body Language of Fear in Dogs from How to Behave So Your Dog Behaves by Dr. Sophia Yin, DVM, MS: