Trivia: During filming, Tom Baker (The Doctor) was bitten on the left side of his upper lip by a dog belonging to Paul Seed (Graff Vyda-K). As a result, publicity stills for "The Ribos Operation" saw Baker wearing a plaster on his face, and for the remainder of filming he required heavy and uncomfortable make-up application to cover the wound. The scar remained visible for much of Season 16.
Doctor Who (1963)
1 trivia entry for season 16
Visible crew/equipment: (Ep. 2) When The Doctor, Jo, and Dr. Tyler are taken into Omega's palace, in the first shot of the multiple passageways (right before Jo says that it looks like Aladdin's cave) the curved chalk actor's mark is visible on the floor, then we see it again in three following shots. Note that when they're all escorted further inside, just as Dr. Tyler comments about the matter/anti-matter not making sense, Jon Pertwee looks down, presumably to make sure he hits his mark.
Castrovalva - S19-E1
The Doctor: That's the trouble with regeneration, you never quite know what you're going to get. (00:12:15)
Question: What caused the first Doctor to regenerate? Was it old age?
Chosen answer: No, it was the result of the Cybermen's draining Earth of energy to their world, that also affected the Doctor, draining his energy as well, causing him to regenerate.
Also In the episode it's said that his body was wearing thin.
Dan23