In episode 71 the MTM Kitten was replaced by Miss Moore herself, saying "Th-th-th-that's all folks!", a line spoken by Mary Richards during that episode.
This series introduced the MTM Productions logo at the end - a tiny, meowing kitten. This is a parody of the MGM Studios roaring lion. The kitten logo (or variations thereof) would be used throughout the 1970s and 80s on a number of different TV series.
Throughout Season 5, scenes of Mary and Rhoda walking down the street can be seen in the opening credits for a few episodes despite Rhoda having moved to New York.