These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Recycled Script: An early episode had the roommates trying to hide a recently adopted pet from Mr. Roper. Towards the end of the series' run, a similar plot (with a different animal, Mr. Furley and Terri) was used. John Ritter himself later acknowledge the trope and felt this was when the series was starting to run out of ideas.
Replacement Scrappy: Cindy, Chrissy's cousin, was almost a carbon clone with considerably less jiggle factor and the added annoyance of being The Klutz. Terri managed to avoid this fate by actually having a brain.
Tear Jerker: Mr. Furley recounting how he once had a pet as a kid, but it was hit by a car and died, he then decides to name the cat he found after it.