The duration of the "chickie run" was obviously extended to heighten its tension and dramatic impact. The cars are seen going far too fast, and for far too long a period of time, to cover the distance to the cliff. At the speed they were traveling over the distance involved, they should have gone over the cliff within a few seconds.
When Plato and Jim are at the Planetarium, Plato points to the mansion, located far away in the distance. However when they go the mansion, the mansion and Planetarium seem to be right next to each other, as they can easily run from the mansion to the Planetarium.
When police backup arrives at the Griffith Observatory, the officer approaches the vehicle on the driver's side to talk to the Juvenile Division officer in the back seat. There are two cutaway shots and now the conversation continues on the passenger's side of the car. The officers within the car change sides of the vehicle, too.
During the fight between Buzz and Jim behind the planetarium, Buzz kicks a switchblade at Jim. It rolls on the ground and stops about 3-4 feet in front of Jim. The next moment when Jim picks it up, it's right at his feet.
After Buzz has fallen off the cliff and Jim returns home, the left shoulder of his jacket is dirty. When he lays on the couch it is clean again. As he is arguing with his parents on the steps, when he faces his father, the jacket has the dirt on it, when he turns to face his mother, the jacket is clean again.
During the race scene there's a shot of buzz's left hand cuff caught on a door handle that faces forward. The very next shot shows his left hand on the wheel and his right hand trying to free himself from a completely different door handle that faces backwards. The first door has a stripped upholstery and the next is just plain gray.
When Jim goes to change his shirt before heading to the chicken-run, it shows him talking to his father with his shirt not tucked in. When it cuts to the next scene of Jim walking out of the room away from his father, his shirt is tucked in.
When Plato arrives at the mansion just after Judy and Jim do, after talking briefly, they let him into the house. When he walks into the house and comes up the stairs, a cord is clearly visible dragging on the ground behind him. Probably a cord for the microphone.
After the "chickie run", Jim is shown laying on his living room couch watching his mother coming down the stairs. His head is tilted back, and the camera switches to show the scene from Jim's perspective, with his mother initially seen upside down, then slowly turning to right side up as Jim turns his head. But in the last moment of this shot, Jim's head is shown -- an impossibility since the shot is supposed to show what Jim is seeing.
The goof item below may give away important plot points.
When Plato is lying on the ground dead, Judy has his left shoe in her hand but a shot of Plato shows his right shoe missing. When she goes to put it back on him, it is the left shoe that is off. Throughout the sequence, shots from Plato's head show that his left shoe is off, while in close-ups it is his right.