Continuity mistake: Marshall Dillon buries an outlaw at Sarah's place. He installs a wood cross at the grave. Sarah comes out and they talk. When she leaves, the scene cuts back to Dillon and the cross is missing.
A Quiet Day in Dodge - S18-E19
Other mistake: Festus returns from catfish fishing carrying a gunny sack full of fish that is bone dry when it should be dripping wet or at the minimum damp from the fish.
