Visible crew/equipment: If you look closely behind the log, as Duane and Blaine plummet over the hill in their car, as they chase the key-cutter in the hot air balloon, you can see a ramp placed, however it is painted to blend in with the ground. If you watch closely you can even see it bounce. (01:00:40)
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: As Duane is about to hit the first cow in the field, the direction it is facing changes instantly between shots. (01:01:25)
Visible crew/equipment: When Duane hits the second cow while hanging from the rope, if you watch carefully you can see the head of someone, bent down behind the cow, wearing a white hat. (01:01:30)
Other mistake: In the field, as Duane is flying into the cows, one of the cows jumps "up" before Duane even hits it. (01:01:35)
Continuity mistake: After dropping from the hot air balloon rope, Duane looks up and sees the car with Blaine on the hood, driving towards him. He gets up and starts to run away from the car, and behind the car in this shot is just field - previously there were cows in the field. The position of the cows change in a few following shots too. (01:01:45)
Continuity mistake: In the Balloon Chase scene, if you watch the sky it changes a couple of times. One time it's overcast, the next it is evening and the sky is orange. (01:02:25)
Audio problem: When Duane and the key-cutter are arguing on the cow, Duane cries "Gimme back my key" and then the key-cutter replies "what key?" but his mouth doesn't move. (01:02:25)
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)
Revealing mistake: After Duane falls from the hot air balloon into the oasis, you can see the shadow of the hot air balloon basket, but the shadow of the balloon itself is missing. (01:02:45)
Other mistake: When Blaine is on the hood of the cruise-controlled car, you can clearly see it's headed straight for thr oasis, however in the next closeup, the car smashes into a group of rocks, which were well off to the right of the screen. (01:02:55)
Continuity mistake: When Blaine drives through a wooden fence into the monster truck race, we see the grille of the car intact, but it was seriously damamged, when it hit the rock by the oasis in an earlier scene. (01:02:55 - 01:22:55)
Continuity mistake: At the Monster Truck Rally, the blue convertible that they are driving has no dents or scratches, it looks perfect. But in the scene before that they are doing nosedives into the dirt while chasing the hot air balloon. You can clearly see the damage then. (01:03:10 - 01:27:30)
Visible crew/equipment: When Duane is hanging on the rope, going through the cow pasture, when he hits the second cow you can see a person's hand in the bottom left corner of the screen. (01:04:00)
Visible crew/equipment: When Blaine is on the hood of the convertible and he looks back and sees that no one is driving the car, the view hole for the person inside the seat who is actually driving the car is clearly visible. (01:04:20)
Audio problem: When Owen is fixing the tyre and all the Lucy's come outside, the old Lucy says "Well maybe we should check the oil," but her mouth says a different line. (01:04:35)
Other mistake: When Seth Green falls into a desert oasis, he causes a huge splash, but in the next closeup there's only a few ripples around him. (01:05:25)
Revealing mistake: When Enrico is putting the heart back into the bag, but it flies out of the window, as Zack pulls the van to a halt, you can see fresh tyre marks on the road, in the exact same place, from a previous take. (01:05:50)
Visible crew/equipment: When Enrico and Zack are searching for the heart, a dog comes along with it in its mouth. In the shot of Enrico saying "hello little doggy, hello there" if you look at the big truck parked on the road, you can see a black wire / cable trailed in front of it. This was not there in a previous shot within the same scene. (01:06:25)
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