The Night of the Plague - S4-E24
Continuity mistake: The last scene shows the back of the boxcar amid dirt and brown/mustard colored short grass. When Ms. Averi Trent opens the door to meet her fiancé, we see a lush green tree by the door.
The Wild Wild West (1965)
1 continuity mistake in The Night of the Plague - chronological order
Starring: Robert Conrad, Dick Cangey, Ross Martin, Whitey Hughes
The Night of the Bubbling Death - S3-E1
Revealing mistake: As West drags the body of a bad guy out of the scene, the supposedly unconscious man is holding his head up so as not to have his head dragged through the dirt. A truly unconscious person's head would flop back on to the ground.
The Night of the Infernal Machine - S2-E14
Trivia: West collides with the cook and sends him sprawling face-down in a huge platter of gelatin. Before racing off again, West quips, "Sorry about that, chef!" This was a winking homage to the 60s spy comedy Get Smart and its bumbling hero Maxwell Smart's famous catch-phrase, "Sorry about that, Chief!" (00:47:30)