As you may have realized, yorkies are always on alert when someone new arrives on the scene. They usually perceive people they do not know immediately, however, sometimes they start to growl or bark at some, but not at others. This momentary bad temper could indicate aggression, a defensive attitude or simply some kind of anxiety. But, why do they have different reactions depending on the individual? Could they know something about them that you do not know? Few people can summarize the reactions of all dogs, and definitely, each case is unique, although we can see the way dogs perceive their world and, perhaps, get an idea about this interesting question.
For them, each subject emanates a different scent. In addition, they have a much more advanced sense of smell than that of humans; In fact, they are between 10,000 and 100,000 times better at it. Because of this huge difference, we have a hard time understanding the amount of information they must process when they receive the smell of another person. Surprisingly, trained dogs are able to distinguish between two identical twins from the same environment, even if they have the same diet. To make matters worse, you could know where they have been or with whom.
For many reasons, your yorky might smell something in someone else that would make him growl, even though your human nose could never feel it.