In Pearl's shootout with Lewt, her bright red lipstick disappears in the time from she is between the rocks where she is shooting and when she clutches her shoulder. It's not smeared - it's completely gone without a trace.
When Jesse is sitting in his hotel room, a rock flies through the window, breaking the glass. As Jesse opens the window, a piece of glass falls down and sticks into the lower edge of the window frame. This piece of glass disappears between shots as Jesse talks to the cowboy Sid outside.
As the army of ranchers is riding across the Texas range to stop the railroad from entering Senator McCanles' land, the weather in the sky overhead changes from clear to cloudy to clear again between shots.
When the Cavalry rides off after intimidating McCanles from attacking the railroad because as the Senator says "I fought to defend that flag (the Stars and Stripes)", the music played is "Bonnie Blue Flag", which was an anthem of the Confederacy.