Ascended Fanon: Rainbow Dash calls a certain wall-eyed grey pegasus "Derpy" on-screen. If it wasn't canon before... it is now. Then de-canon'd by Hasbro executives after the "Ableist" Controversy (for lack of a better name for it).
Based on a Dream: According to "The Elements of Harmony: Friendship is Magic", the interrogation scene with Applejack and Pinkie Pie was based on a dream Amy Keating Rogers had when she fell asleep with writers block while writing the episode.
Cross-Dressing Voices: With a bizarre twist. Tabitha St. Germain thought Derpy was a boy and voiced "him" accordingly, putting on her best male voice. Only after the episode's premiere on The Hub did the fans gently correct her.
Played straight in Hungarian, where Derpy was voiced by a man.
Development Gag: The photo of Applejack that Rarity uses is based on Lauren Faust's concept sketch of her.
Fandom Nod: Considering that this episode canonized Derpy, it can't be coincidence that Dinky Hooves and Carrot Top (who are closely associated with Derpy in Fanon) make several cameos and can even be seen together when Applejack's train leaves, sitting in the train car that Derpy appears in during the season 2 opening sequence and the previous episode.
Keep Circulating the Tapes: If you preferred the original version of Derpy's scene over the edited version, then you'd better keep a vicegrip on that Friendship Express DVD—it's the only place (outside of DVRs and YouTube uploads) you'll be able to see it. Strangely, while the episode on Netflix is edited, the closed captions still refer to her as "Derpy".
Old Shame: The creators publicly apologized to both sides of the flame wars caused by Derpy's edit.