Catch A Falling Star - May 21, 1979 - S2-E10
Character mistake: In the preview for this episode, Charlie has trouble getting his countdown straight. He shouts that Sam is on in 50 seconds, then 47, then 48. In the episode itself, the mistake is corrected with a rather obvious overdub, changing the final number to 43. (00:02:05)
Hercule Poirot's Christmas - S6-E1
Character mistake: After Japp's arrival, when Poirot walks up the stairs with the two male detectives, at one point he says "Mais no madame." ("But no mylady.")