The Wild Wild West (1965)

The Night of the Avaricious Actuary - S4-E11

Continuity mistake: The letter from the Cyclops Insurance Company that Gordon pulls out of his pocket is folded, wrinkled, and well-worn. In the close up of the same letter West reads, the letter is white, pristine, and not wrinkled or folded.

The Night Dr. Loveless Died - S3-E4

Trivia: Dr. Loveless' uncle's name, "Liebknicht", is, aside from the addition of the letter "k", German for "Loveless".