i personally think that horn doesn't control dragons like a remote control so much as keep the dragon from harming and killing the possessor of the horn. this is a huge deal, it suddenly makes them very trainable. if someone gave me a horn and it made it so that i knew 100% a lion wouldn't hurt me, i could train the lion, once the danger is gone anything is trainable. and from what we see of drogon and danny is that dragons seem to have a fairly high animal intelligence. i'd say anywhere from dog (german shepherd level perhaps) to a dolphin or primate.
