On both front fenders of Stephanie's van, "Parties Catered" is misspelled. Perhaps Stephanie made the mistake herself or the filmmakers just didn't notice it, but sure enough, the van says "Partys Catered".
When Number 5 is driving and listening to the radio, we see the first radio station that he listens to, that is carrying a horse race, is at frequency 94.1. After changing the settings 2 times, he stops at a radio station that is playing music, but the frequency is back to 94.1.
When Ben is draping a tie around Crosby's neck near the beginning, the two ends of the tie start off hanging straight down, in the next shot they are crossed over, and in the next shot they are uncrossed again.
When the two buses arrive at NOVA to deliver the crowd of spectators from the testing range, the first has a blue stripe and the second red. In the next scene both are red. The first shot is also a different make and model from a different bus line as well. The blue bus is a GMC in RAI livery while the red buses are both Silver Eagle units in Trailways livery.
After Number 5 lands on top of Stephanie's truck, when it arrives at her home he is still watching from the roof. But in the shot when Stephanie is talking with Mrs Cepeda, the truck is visible in the background but Number 5 is not there. Then in the following shot of the truck, he is visible again.
When the NOVA security force is 1st pursuing #5, when the "Ferret" armored car hits #5 on the bridge & he raises his head to look into the vehicle, the driver slams the protective cover shut. In th next shot when #5 is flying off the bridge, the cover is open again.
When Newton is driving the NOVA cube van at night, Ben reaches over to turn on the headlamps, but the switch on GM based vans and cab-and-chassis is located to the left of the steering column - totally out of reach of the passenger.
When Crosby is in the lab programming the robot arm to play the keyboard, another arm answers the phone for him and then hangs up, both on command. As Crosby gets up to leave, you can see the arm behind him picking up the phone receiver again, although there was no incoming call.
When Stephanie is in her kitchen cooking something in a pan, she offers the stirring spoon to a pet skunk to taste it even though it is obviously steaming hot and would burn any animal's mouth that touches it.