Smough laughs during the battle occasionally, though it may be quiet, it is a distorted version of the Fat Official's laugh from Demon's Souls. When I was facing Super Ornstein, I realized that you can still hear Smough's laugh. So I was thinking, did Ornstein transfer Smough's soul into his body? It would make sense because Super Ornstein performs one of Smough's attacks.
We know that Smough had always wanted to be one of Gwyn's best knights, So did Ornstein allow Smough to take control of his body so that he can become the knight he had always wanted to be instead of being the first to die in shame? I guess Ornstein may have respected Smough and had somewhat knew his pain of not being in the high ranks, for Smough was simply an executioner.