One of the fascinating pieces of trivia below is true*, the other is false. Do YOU know which is which?

Back to the Future (1985)

1) Michael J. Fox had always been the first choice for Marty, but he was unavailable due to scheduling conflicts with his work on Family Ties. As “Family Ties” co-star Meredith Baxter was pregnant at the time, Fox was carrying a lot more of the show than usual. The show’s producer Gary David Goldberg simply couldn’t afford to let Fox go. Zemeckis and Gale then cast Eric Stoltz as Marty based on his performance in Mask. After four weeks of filming Robert Zemeckis and Bob Gale felt that Stoltz wasn’t right for the part and Stoltz agreed. By this stage, Baxter was back fully on the show and Goldberg agreed to let Fox go off to make the film. Fox worked out a schedule to fulfill his commitment to both projects. Every day during production, he drove straight to the movie set after taping of the show was finished every day and averaged about five hours of sleep. The bulk of the production was filmed from 6pm to 6am, with the daylight scenes filmed on weekends. Reshooting Stoltz’s scenes added $3 million dollars to the budget.

2) In an early draft of the script, the time machine was an old church organ that ran “on the steam of teenage lust,” according to Doc, which is why he befriended Marty. It was Christopher Lloyd’s idea to change the time machine to a car, but the sexual tension between Doc and Marty was kept essentially intact.

*true trivia courtesy of IMDB.com