My son is fascinated by animal torture?

Well, my 13 year old son watched a video about animal torture and now he draws morbid pictures of dead animals. I asked my husband about it, but he said it's probably just a stage and he'll grow out of it soon. Yesterday, I seen him nailing a bird to a tree and by the time I got out there it was already dead, but my husband still says it's just a stage and he'll grow out of it.. Is my husband right or do I need to seek professional help for my son?