Why do people "kill" that which they do not understand?

Jessica is a 16 year old girl growing up in a rough neighborhood where there are plenty of knives and guns lying around and the city is full of ravenous dogs. One day Jessica was walking down the street when a strange animal jumped out of the bushes, It was a cute little kitten but Jessica had never seen a cat in her life, instinctively she pulled out her pistol and put two into the chest cavity of the cat.

This short story seems to make no sense. But living in fear must have drove her to the point of bigotry, where she considered everything a threat. A closed mind? Non-negotiable? So I ask where does the "kill" come from?