Continuity mistake: On the truck cab's rear window, there is some sort of air conditioning unit installed. In some shots, such as the gas station scene where David Mann is on the telephone, or the railroad crossing scene, the air conditioning unit has a support structure to hold it in place. In the rest of the film however, there is not any support structure to be seen.
Trivia: At the end of the film when the truck goes off the cliff, we hear an odd groaning sound. This is a dinosaur growl from an old movie Spielberg likes. Interestingly, this same sound is also used at the end of Jaws as the shark sinks to the bottom of the ocean. Spielberg did this to show that Jaws and Duel would always be closely connected.