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)
Visible crew/equipment: As Nick puts his coin into the machine to gamble, you can see the crewmembers arms pushing equipment along, reflected in the golden edges of the casino machines. (00:13:30)
Visible crew/equipment: When the lady trips on the glass and rolls down the stairs, you can see the ankle pads she's wearing. (00:06:55)
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)
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)
Visible crew/equipment: As everyone is leaving the casino and are starting the race, as Vera and Merrill walk out the double doors you can see a crewmember and the camera, which is pulling backwards, reflected in the other closed door. (00:23:05)
Visible crew/equipment: When Vera and Merrill crash into the pile of cars, a skeleton rolls out of the back of the car in front of them. Then in the next shot the skeleton falls downward, and as it does you can see a thin metal wire attached to the back of the skeleton, obviously used to control it. (00:53:25)
Visible crew/equipment: When the rocket car zooms past the repair mans garage and it collapses, you can see a wire running across the outside of the garage, from above the window to behind the petrol pump, and there is a white cable trailed across the road to the left of the garage - in an earlier shot you can clearly see these were not here. (01:16:00)
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)
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: The safety wire attached to Blaine's right side is visible when he notices the rope around the radar tightening, and gasps / flinches. (00:30:10)
Visible crew/equipment: In practically every scene throughout the movie the reflection of blue screens and reflectors are visibly reflected in Vera's glasses. (00:07:35)
Visible crew/equipment: When the gang run toward the Silver City Station, they reach the door, struggle a little (as they're all fighting over getting inside) and then they enter. As they arrive at the door and then struggle, from the shot inside you can clearly see the reflection of the camera in the glass of the door. (01:29:10)
Visible crew/equipment: When Vera and Merrill go zooming past the car repair man's garage and the garage collapses, as the man turns and mutters "whoa," the camera's shadow is clearly cast on his back. (01:16:00)
Visible crew/equipment: The shadow of the camera truck is visible in the cow pasture.
Visible crew/equipment: In the wide shot as Duane and Blaine drive up by the pierced girl's red car, you can briefly see a reflector, equipment and some crew reflected in the car. Then when it cuts to a close-up, you can see the reflections in the side of the wing mirror. (01:21:35)
Visible crew/equipment: When Tracy throws the fire extinguisher into Sean's truck, and it goes off, sending CO2 gas everywhere, you can see the thin black tube running across the pavement, to under the car, presumably used to spray the gas out of. That tube wasn't there earlier! (00:44:40)
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