Continuity mistake: When Jack and Mrs. Pendrake meet in the whorehouse and talk through a screen of glass beads, Jack is standing very close to the screen, that's why it's out of focus when the camera is on her "looking through his eyes". However, in one shot it's not, and that looks quite strange because Jack hasn't moved away from the screen.
Factual error: The worst historical distortions in this film must concern legendary "Wild Bill" Hickock. First of all he wasn't killed by a teenage boy, but one John McCall, a man in his 30's. McCall sneaked behind Hickock who was in the middle of a poker game and shot him through the head killing him instantly. Secondly this took place on August 2 1876, about five weeks AFTER the Custer's Last Stand.