The Rex Montana Story - S1-E35
Revealing mistake: When Flint follows the Indians, there's a strong wind blowing. But the two puffy clouds in the backdrop sky never move.
Three Bells to Perdido - S1-E1
Visible crew/equipment: When Paladin talks to the ranchers, two equipment shadows are moving on the wall at the upper left of the screen. (00:03:00)
Revealing mistake: After he's ambushed and killed in the alley, the "dead" sheriff can be seen breathing quite healthily.
Adios, Señor Magistrado - S1-E26
Character mistake: During the tavern meeting, Sergeant Garcia calls Magistrado Carlos Galindo "Comandante."