This is a term used to describe one of "three warning signs", or behaviors of Sociopathic behavior. Zoosadism is the excitement or pleasure, (sexual or otherwise) experienced during the act of inflicting cruel, torturous, and even deadly acts on animals. Research has found a direct link between this response, the perpetration of the acts themselves, (harming animals during childhood), and an increased probability of committing serious aggression towards people, usually those weaker than themselves. This has been studied and researched since the early 1960's according to the details I was able to find. For more details, please see the sites listed below.