Paul McCartney and Linda McCartney agreed to lend their voices to this episode on the condition that Lisa remained a vegetarian throughout the rest of the series. By this time, every surviving member of the Beatles at this time have guest starred on The Simpsons.
In the closing credits where Paul McCartney sings "Maybe I'm Amazed" there is a background voice. If you play it backwards it is a recipe of Lentil soup read by Paul McCartney. At the end of the Lentil soup recipe, Paul McCartney adds, "By the way, I'm alive." This is a reference to the belief from the late 1960's that if you played the end of The Beatles song "I'm So Tired" backwards, you could hear John Lennon moaning, "Paul is dead, man; miss him, miss him."
In the DVD audio commentary for the episode, David Mirkin called the opening sequence at the petting zoo one of his favorite set pieces in the show's history. He thought it was "absolutely hilarious", and praised Mark Kirkland for his animation. Mirkin also enjoyed the use of Apu in the episode, because Apu shows Lisa that "the way to get people to change is through tolerance and understanding".
The idea for the episode came to David X. Cohen while he was working on another script for the show. Cohen could not concentrate on his task because he was waiting for lunch, and on the back of the script he scribbled, "Lisa becomes a vegetarian?" Cohen showed the note to writer Brent Forrester, who liked the idea. Show runner David Mirkin then approved the story when Cohen pitched it to him. Mirkin had just become a vegetarian himself, and later noted that many of Lisa's experiences in the episode were based on his own.
The designs for Paul and Linda McCartney are unusual for the series in that the characters have brown and blue irises, respectively. Most characters simply have black spots in the centers of their eyes.