Continuity mistake: When Nick and his friend are talking in the hotel lobby about breaking rules, the extras in the background change in every shot, some passing twice, some jumping location, others appearing and disappearing. (00:11:10)
Continuity mistake: The knot in the rope and the way the rope is tied around the bumper of Duane's car, in the scene where they break the radar, changes between shots. (00:30:15)
Continuity mistake: When the bikers destroy Hitler's car, they break off the front left flag. Later, when Hitler's car crashes into the WWII veteran convention, the flag is back. You can also see it is back later when the people come to collect it from the diner car park. (01:07:40)
Continuity mistake: When Duane and Blaine are chasing the key-cutter who stole their key, they drive over the same hill and land twice - note the same tree stump they pass twice. (01:00:40)
Continuity mistake: Throughout the chase-after-the-hot-air-balloon scene, the hood of the blue car that Blaine and Duane drive differs from dusty to sparkling clean from shots. (01:00:55)
Continuity mistake: When Donald Sinclair explains the race, he explains that they have 1 in 6 chance of winning, same as a die roll, then he rolls the die. Later in the scene, the die has vanished without anyone moving it.
Continuity mistake: When Owen is sitting at the bar, and the TV has him featured as "Loser of the Week," the same woman in a blue top, carrying a handbag and blue cardigan walks past him twice. (00:05:10)
Continuity mistake: As Vera and Merrill drive down the road and then turn right, down the shortcut just past the yellow sign with the graffiti on it, there is no front licence plate on the car. However, as the car rolls down the hill, there is a white plate fixed on. (00:52:45)
Continuity mistake: When the rope tied around the radar pulls Duane's truck forward, in a wide shot the sky is crystal blue and totally clear. Once the truck has been pulled to the top of the tower moments later, in another wide shot the sky is now filled with clouds. (00:30:30)
Continuity mistake: Duane sprays the key-cutter's face with milk from the cow's udder, and his face is wet, and covered in white milk, but in the next shot the white milk has gone. (01:02:35)
Continuity mistake: Tracy's hairband keeps changing colour throughout the movie. At the airport its a white scrunchy and in the helicopter it starts off black, and then goes to light brown. (00:27:35)
Answer: They only had blanks - the non-cut keys that are used to make keys. So when they saw those, they knew that the guy had their key.
wolfchild