A proper noun doesn't just tell what something or who something is, it tells EXACTLY what or who it is. So for example : We went to the resturaunt is a noun, but we went to Mcdonald's is proper.
I wanted to say it spita. but could be wrong
Mary Brown's dog symbolizes the child in a way the police can get away with the killing even if the child or citizens are innocent.
The police showing no remorse about killing an innocent life of the dog/child demonstrates the corruption of the environment there.