I find it interesting to watch how people treat animals. While we are given them by God for humane slaughter as a source of food, some people are cruel to them, and it reveals something about their hearts. God would say, 

"A righteous man has regard for the life of his animal, But even the the heart of the wicked is cruel." (Prov 12:10)

Compassion and kindness to animals is a trait that God looks for. Lots of serial killers even start their road to evil by abusing animals. These little things can reveal parts of a person's inner man.