Anthropologists have really figured out that dogs respond quicker to visual cues than verbal. This makes sense because in the dog world, that is how they primarily communicate. Some people might think they communicate through barking but that is a more minor part of communication. Dogs see other dogs and naturally assess whether their ears are up or forward or down. They’ll look at the tail. Is it wagging and how is it wagging? They’ll also look at other dog's approaching. Is it coming straight for them, suggesting aggression, or is it approaching in an arc and not directly communicating friendliness or no threat?
Consequently, it is important that every dog owner educates him or herself and becomes fluent in canine body language. That way you can really know what your dog’s state of mind really is.