Why Your Dog Growls At Some People And Not Others

Some people just look shady.

Some people look frightening to certain dogs. Dogs depend on their vision less than their sense of smell, but still to a significant degree. Dogs use facial recognition to communicate with each other and human beings may not see facial features in the same way as dogs.  When your dog growls at one person and not another, it might be that he sees a feature that is reminiscent of a threat to him in his memory.