Most of our encounters with other peoples’ pets occur while dogs are being walked on a leash. If you choose to approach a dog but something about the animal communicates unease — even if the owner is telling you their dog is friendly — go with your gut.
Both the dog and its owner are sharing their truth from different perspectives: The dog is communicating how it feels right now while the owner is telling you what they know to be true most of the time.

Regardless of breed or temperament, all dogs draw from the same behavioral catalog to express social discomfort. In the list that follows, check marks correspond to the physical cues conveyed by the dog in the photo. Unfortunately dogs that look like this trigger human sympathy, drawing us closer. Our bad.
Show whites of the eyes ✓
Cower, low body posture ✓
Tuck tail or draw close to body (if not low-set for breed) ✓
Ears low and/or back ✓
Freeze, overall body tension ✓
Back away
Pace
Lick lips, yawn
Piloerection (hair along back and neck raised)
Hide behind owner or furniture
Bare teeth
Growl, bark
Lunge
"To say nice dogs could never bite is to say nice people never argue." — Unknown
Whether alone or in the company of your dog, use best judgment and err on the side of caution. Paying attention to canine body language will go a long way to keeping dogs under threshold and safe. Your dog will thank you for having their back.