In my hometown, people often go to buy dogs. People who buy dogs often ride motorcycles carrying an iron cage and some tools to catch dogs. Every time that person passes in front of the gate, my dog barks very loud and seem very angry with that person. Although from a young age it only stayed at home and never came into contact with the dog buyers. I don't understand why it has such an expression. The road in front of the house is about 50 m from my gate. I think that in some way dogs have communicated information to each other about the dangers of people buying dogs. Is there any other explanation for this story?