Paul McCartney's 1990’s appearance on The Simpsons came with conditions.
Series producer David Merkin went to London to record voice tracks with Paul and his first wife Linda, whoplayed themselves in the episode. They agreed to appear in the episode, which had Lisa Simpson becoming a vegetarian, on one condition: that her character would stay on a meat-free diet.
That wasn't a problem for Merkin, who follows a vegetarian lifestyle and kept Lisa on one. (London Express)