In the episode, "Dear Mildred", where Radar gives Potter the horse for his anniversary, watch the part where BJ and Hawkeye are trying to give the horse an injection to calm it down before surgery. Radar has a hold of the halter (which, by the way, where did a leather halter come from in the middle of Korea?)and if you watch him during the entire scene, you'll see him purposely backing the horse up and pulling him forward to make the horse look like he's being unruly. He tries to block the yanking and pulling with his arm but you can clearly see Radar making that horse go back and forth by pulling on the lead rope.