Smelly Cat first appeared in the second season episode "The One With The Baby On The Bus" where it was revealed to be Phoebe's most popular song. At the end of the episode she teaches musician Stephanie Schiffer (played by guest star Chrissie Hynde) to play the song. In "The One Where Eddie Moves In" Phoebe makes a professional recording of the song for possible commercial release, though her voice is replaced by an older singer. A short video for the song also appeared in this episode and is included in full as a bonus feature on the second season DVD set. In "The One With Phoebe's Ex-Partner" a character played by guest star Elizabeth Daily uses the song as a jingle for a cat litter commercial.
In the fifth season episode "The One With Joey's Bag" Phoebe meets her estranged father, who reveals he sang a lullaby to her when she was a child, called "Sleepy Girl", which has the same melody as Smelly Cat. The "Smelly Cat Medley" track on the Friends Again soundtrack, credited to Phoebe Buffay & The Hairballs (featuring the Pretenders), features a recording of the scene, and then a new, more artistic recording of the duet between Hynde and Phoebe. Hynde then launches into a hard-rock version with new lyrics. The song became so famous that a group of Portuguese comedians had elected Gato Fedorento (Smelly Cat in Portuguese) for their show's name, claiming they were fans of Friends. Also when meeting Mike's parents, she sings it to them during dinner because nobody had spoken in seventeen minutes in "The One With Ross' Inappropriate Song".
Smelly cat, Smelly Cat,
What are they feeding you?
Smelly Cat, Smelly Cat,
It's not your fault!
They won't take you to the vet,
You're obviously not their favorite pet,
May not be a bed of roses
You're no friend to those with noses!
I promise you before we're done
All the world will smell as one!