The only time during the theme song credits where the cast is shown in their "alternate lives" persona.
The unusual chair in Joey's apartment is also seen in Lt. Worf's quarters in Star Trek: The Next Generation (1987).
In the real reality, Carol's hair is straight, while Susan's hair is curly. In this alternate reality episode, their hairstyles are reversed.
In the 2 part split version of this episode: Part one features the usual variation of the standard version of the opening titles, with the "Fat Monica Dance" under the closing credits. Part 2 starts immediately with the specially re-shot "Alternate Reality" version of the Fountain Titles.
The couch that's seen in Monica's apartment throughout this episode (and the episode prior) is the same couch that Ross purchased and attempted to move into his apartment during season 5 episode 15 "The one with the girl who hits Joey".