When we gaze at something or someone we love, a chemical reaction takes place within our body. Dopamine and serotonin are released into our system and cause a chemical reaction that leads to feelings of happiness and joy.
The same thing happens when you look at a person you do not like. Except in this case the body releases a completely different set of hormones that are associated with hate, resentment and fear. Your dog can detect these changes in you, and will most likely begin to dislike the person that caused your reaction.
Of course, body language plays a role in whether your pet thinks you like someone or not. Keep in mind that any dog, even a gentle dog, may try to protect you from people it perceives as a threat.
If you are avoiding a person, watching that person closely, or are otherwise sending out signals that you distrust someone, don’t be surprised if your dog barks, growls, or lunges at that person if he or she tries to approach you.