When Princess Penelope first appears on screen Lisa is reading Angelica Button and the Infinite Armoire by T.R Francis. The Harry Potter parody first appeared in The Haw-Hawed Couple (2006)
This was the 450th episode.
Eartha Kitt & Anne Hathaway have both played Catwoman. Kitt in Batman (1966) & Hathaway in The Dark Knight Rises (2012)