When Ike informs the other riders that Buck slipped out overnight and starts grabbing his clothes, Jimmy says, "You can't; you don't even know where he went." However, Ike had not signed anything prior to this, so Jimmy's protest was not in response to anything. Furthermore, the line did not sound like Jimmy's voice before or after it. So it is clear that the line was dubbed in to give the impression that Ike had signed that he planned to follow Buck.