Both Edward Hardwicke and Jeremy Brett hated the toupee Hardwicke wore for the first few episodes. Brett went so far as to nickname it "Roland" after the Roland Rat character in a children's TV series of the same name.
David Burke left the role of Dr Watson after the first season, as he was offered a position with the Royal Shakespeare Company.
Despite Edward Hardwicke playing Watson in the second season, the flashback shows David Burke playing Watson.
Because Edward Hardwicke was substantially shorter than David Burke, his shoes were fitted with lifts. These proved to be a disaster when they filmed a scene in rain and mud - the lifts had no traction and Hardwicke kept slipping. Eventually the lifts were discarded.
Holmes describes Colonel Moran as a "shikari". A shikari is a big game hunter or hunting guide in India.