The highly-anticipated appearance of Paul and Linda McCartney on the show coincided with Lisa's choice to become a vegetarian. What distinguishes this development from most other shows at the time was that Lisa's vegetarianism was a permanent character change and not one of those 'story of the week' things. This development was a combination of the writer's wanting to push Lisa's character into new territory and a special request from McCartney himself. Some of the writers were inspired from their own vegetarian experiences and thought that the episode would not only be a good spotlight for Lisa, but it would probably appeal to McCartney's tastes. For those who don't know, Paul is a committed vegetarian, an animal activist, and a long-time Simpsons fan. Upon being contacted, Paul was open to appearing on the show but only if Lisa became (and remained) a vegetarian for the rest of the series' run. Naturally, the writers obliged (who could say no to a Beatle?) and Paul got to appear on one of his favourite shows with his wife whilst spreading a positive message about vegetarianism and animal rights. This proved to be a positive change as not only did Lisa's vegetarianism help further define her character, but it also opened up other avenues with the character in which the writers could impart nuggets of intelligence and social awareness to various issues.