Quote:Kittens play, but cats have no sense of humor at all.
Play serves largely to reinforce social connections, of which adult cats (except in domestication) rarely have any. Q: do adult lions exhibit play behavior?
As to the addiction question: it seems to me that our attraction to addictive substances proceeds in spite of, rather than because of, our knowledge the ill-effects. Why do we try them? Why, because other people do, and like it. Animals exhibit the same sort of behavior: if one of my dogs finds a tasty pool of vomit in the park (gross but true) the other will see her wanting to eat it and will exhibit the same behavior. The visceral desire to feel good is deeper -- and so more ancient, and so more common to animals -- than our ability to reason through consequences and shape our behavior accordingly.