Cats/YMMV

Adaptation Displacement: The lyrics were lifted from T. S. Eliot's poems, mainly from the book Old Possum's Book of Practical Cats. Guess which gets more exposure?
Alternate Character Interpretation: A big part of the fandom, especially where Macavity is concerned.
- The Rum Tum Tugger and Mistoffelees are a particularly confusing instance. RTT sings Mistoffolees' song, and it's commonly accepted that they're friends, at least until you remember that in RTT's song the chorus goes "The Rum Tum Tugger is a-" and Mistoffelees shouts "...terrible bore!" Fans are divided on their relationship with one another.
- Word of God says that Mistoffelees and the Tugger are two of a group of four brothers (the other two being Munkustrap and Alonzo), and this forms the basis for their love/hate relationship. It also explains the reactions of Munkustrap and Alonzo to the Tugger and Mistoffolees, and vice versa.
- This can often be for any of the characters and relationships, since each production and country does it slightly differently, e.g., who Victoria does her "Sexual Awakening" dance with, who Alonzo gets paired with (Demeter or Cassandra), and which cats are in the cast, often "Swing Kittens" like Etcetera, and Electra, or the London Swings (e.g. the 'Brown Queen') can be left out (due to some of them originally being actors/actresses other cats characters outside of songs (Rumpleteazer/Etcetera, Quaxo/Misto for example), so Rumpleteazer and Tantomile can be members of Rum Tum Tuggers screaming fan club. What fans use as "their canon" can depend on which country they're in, which productions they've seen, and whether they own the filmed stage version.
  - Not to mention the fact that the chorus cats are rarely given much personality other than, well, cats. The ease of Alternate Character Interpretation in this show is great fodder for fanficcers.
Ear Worm: So many of them, but mainly "Memory".
Epileptic Trees: Regarding the relationships (familial & romantic) of the Jellicles (and Macavity).
Everyone Is Jesus in Purgatory: A common interpretation is that the play takes place in the afterlife - Jellicle being " 'gelical", or Angelical, and they recount their mortal lives as a reason they should be allowed to be reincarnated.
- It can be argued that the whole thing is about Sanctification by Grace; the cat who is chosen to be taken up to the Celestial Lair isn't the clever Mistoffeles, the charming Rum-tum-tugger, the wise Deuteronomy, or even Jennyanydots with her good works--it was Grizzabella, mangy, skanky Grizzabella, the cat who NEEDED it most. T.S. Elliot was one of the foremost Christian poets of the 20th C. Andrew Lloyd Webber's father was formerly Assistant Organist at St. Paul's Cathedral; he himself had been a choirboy at Westminster Abbey. I don't know what Lloyd Webber's adult spiritual affiliation is, but he was brought up in a Christian atmosphere.
Ho Yay: Here and there, but mostly between Mistoffolees and the Rum Tum Tugger.
Unfortunate Implications: "Now the Peke, although people may say what they please, is no British Dog, but a Heathen Chinese."
- Possibly justified in that the lyrics were written during a time when they would have been considered acceptable. However, since other Unfortunate Implication lyrics were changed during the course of the show's run (ex. original lyric "The Chinks they swarmed aboard" was changed to "The Siamese swarmed aboard), this could probably have been avoided.
  - It's particularly ironic that Growltiger's Last Stand is one of the most popular numbers in China and Japan.
- Black actress Femi Taylor playing a cat named... wait for it... Exotica. Ouch.
- Jemima's name was changed to Sillabub in the Broadway version of the play to avoid any Unfortunate Implications associated with the name Jemima.
The Woobie: Grizabella