The end credits separate the cast and characters into the three mini stories making up the episode: "Clay", "Smeddum" and "Greenden".
What this means is that some characters/performers are credited more than once if their character appears in more than one "story". Fulton Mackay as "Alec Webster", Bill Fraser as "Murdoch" and Joan Fitzpatrick as "Mrs. Murdoch" appear in all three stories, and so are listed three separate times in the end credits. Meanwhile, the characters of Bill Gavin as "Doctor" and Eileen McCallum as "Meg Menzies" also appear twice (in "Clay" and "Smeddum") and so receive two credits.
For clarity, all of these performers are credited only once on the IMDb cast listing.