In the bar fight in Turley, the bad guy breaks the bottle with his right hand, but when he lunges at Mal, it's in his left hand. [There's plenty of off-camera time for him to switch hands. Maybe he's left-handed, and broke the bottle with his right because it was closer to the bar.]

When Mckendricks men order Mal and Ezra Johnson off Ezra's Homestead Mal Asks one of the cowboys "Do you know what a Henry rifle can do in the hands of someone who knows how to use it?" Ezra is unarmed with his right side facing the camera. In the time it takes the cowboy to answer "Who would that be, You?" Ezra (who is sitting double on Mal's horse) produces a Henry rifle and throws down on the cowboys it wasn't in his right hand in the preceding scene and if it was in his left he'd have to pull it over Mal's head and switch it to a right hand grip to be in position to cover the cowboys (presumably while they sit there and let him do it) there wasn't time between shots. [The rifle was resting on the horse between the two men, right where he could grab it quickly.]

Mal's rifle switches between the Henry 1860 and 1866 models in various scenes [Mal and his father both owned Henry rifles when Mal's father is killed, and Mal inherits his fathers rifle. And Mal also does carry both at times.]

In the scene when the bad guys are going to burn down Kate's house, they throw a kerosene lantern to start the fire. Pause the film right before they throw the lantern and then advance frame-by-frame. You can see the fire start from behind the bookcase a couple frames before the lantern hits the bookcase. [You cannot "see" any such thing. Four frames - one eighth of a second - is the limit of 'persistence of vision', which permits us to "see" 24 still photographs as one second of movement. A mistake encompassing "a couple of frames" is not a mistake - it is part of the film-makers technique to fool the human eye and brain into thinking they see movement where none exists, and in this case he succeeded.]

After the Glover fight scene when Cleese tells him to leave, Glover walks back to the bar to drink the whisky. Listen for the distinct sound of swallowing/gulping before Glover puts the shot glass to his mouth. After his drinks, there is no sound at all. [I think the sound referred to is as Glover first grasps the shot glass - and it's the sound of a heavy shot glass sliding a tad on the thick wooden bar.]

In the scene where the sheriff (John Cleese) is playing chess in the jail, if you look carefully you will see that it's a reproduction of the famous Isle of Lewis chess set that is sold by the British Museum. One would wonder - especially since the original hadn't been found yet - how it got to the Old West. [Not too difficult, in fact. The Isle of Lewis chess pieces were discovered in 1831, and were famous throughout the whole of the British Empire within a few years. The sheriff is obviously English, so why couldn't he have brought his chess set - obviously a treasured possession - with him when he came to the US?]