NORMAN – Jackson Arnold’s frustration bubbled to the surface as he walked back toward Oklahoma’s sideline early in the fourth quarter. Arnold took off his helmet and held it above his head as he looked up and bellowed into the void, at no one in particular – except perhaps himself. The Sooners’ sophomore quarterback, who’d looked more comfortable and decisive for much of the game against Tulane, just committed a near-catastrophic mistake: a pick-six that cut OU’s once 21-point lead down to five with 14:20 to play. Arnold shrugged in disbelief as he took a seat on Oklahoma’s bench and prepared to regroup.