Marty's letter
From Futurepedia, the Back to the Future Wiki
On the eve of Marty McFly leaving 1955 for the future, he wrote Doc Brown a letter on letterhead from Lou's Cafe and sealed in an envelope with the instructions not to open until 1985. It alerted Doc to the Libyan terrorists that would eventually shoot him back at Twin Pines Mall.
When the 1955 Doc discovered the letter, he tore it up, but sometime in the 30 years before the event, Doc taped it back together and read it. Following its instructions, he wore a bulletproof vest on the night of the world's first temporal displacement.
[edit] Appearances
[edit] Behind the scenes
Bob Gale was surprised to get a letter from a young fan in Japan who pointed out that Marty's letter looked different in 1985 than it had in 1955. "Some people don't have enough to do, I guess," commented Gale. Basically, the letter in the first scene concludes with four lines ("Please take whatever/ precautions are necessary/ to prevent this terrible/ disaster"); when Doc taped it back together, the same sentence was on three lines, as seen in the image above. Like the DeLorean odometer, the McFly family candy jar, and the flaps on the shirt pockets, the letter is one of the continuity errors that fans of the films enjoy spotting.
