peaceseeker

Hi I'm well deep into chapter 3 now and have tamed the white arabian as well as the other one by the lake with little to no problems, so I wished that I bring warped brindle arabian by the Wapiti reservation to my collection. Boy was I wrong...This horse buckles me no matter what I do. I'm playing on PC so I keep S pressed down and normally as with the other horses I press A and D in the opposite direction of the horse's movement. I also keep pressing G to calm the horse but nothing works. After 5 seconds the horse buckles me from his back. I wonder is there some kind of trick with this horse, am I missing something or is just my lack of skill? Any help appreaciated