Zoosadism is pleasure derived from cruelty to animals. It is part of the Macdonald triad, a set of three behaviors that are considered a precursor to psychopathic behavior.
Why do I enjoy torturing small animals?
They enjoy hurting things — because it makes them feel powerful. They simply enjoy pain and violence. This group of people suffer from serious psychological problems that will probably not go away on their own. Psychological intervention is essential for them.
Is it normal to want to hurt an animal?
It's not a typical dinner table conversation, but its completely normal to be overwhelmed by your dog's cuteness to the point of wanting to squeeze, bite, or hurt it. The difference is that you don't actually do it (that would make you a psychopath, and a terrible human being).