I know I'm about a year late in helping with this but I think I have a solution to your problem, as well as the problems of others. When you click on the actor (in your case, the animal companion) look under where you put in the name, etc. There's a button that says dialogue; click it. Now the fun part: Experiment! I gave my wolf follower an actual voice, as if he was a human(oid) follower. The reason you can't make the animal a follower is because you need dialogue to get the relationship started. You can't access the dialogue because it hasn't been added yet. Fix that, hit the right buttons and click the right things, and you've got a new pet to love, cherish, and kill with!