What is the significance of the pair of “backwards 9s” of fire left behind when the DeLorean is struck by lightning?
When the big bolt of lightning hits the DeLorean, it sends the flying vehicle spinning on its axis. As we already know, the DeLorean leaves fire trails behind it when it travels through time. Since in this case, the car was spinning, the fire trails are left behind as spirals instead of the usual straight lines left behind when the car is moving straight ahead.