When the runaway car is careening down the mountain, George is almost strangled by Blanche as she hangs on to his tie while flailing around in the back of the car. George's tie is clearly loose around his neck in several shots. When he crashes and climbs out of the car, the tie knot is perfect.
When Maloney and Adamson are in the back room of the jewelry store, Maloney takes all but two cigarettes from the cigarette bowl. However, minutes later, the bowl is full again.
George removes the cap of the ketchup bottle twice between shots when he and Blanche are eating in Blanche's kitchen.
The amount of beer in George's glass at the diner, while waiting for Maloney, increases after he takes a drink.
One of the FBI agents opens the door to the helicopter in a high shot and a man can be seen in the helicopter window (possibly a stunt double); however, in the next shot, it is a completely different man. The same error occurs when the helicopter is seen taking off.
When Blanche and George finally crash coming down the mountain, the car ends up on its side. Coming down the mountain at high speeds, there were several instances when George hit the guardrail hard enough to damage the metal or, at least, scrape the paint off the side of the car. Yet, when the car comes to rest, there is no damage to the car.
As George and Blanche careen down the mountain without brakes, they drive up a sloped embankment. The first slope heading down the hill is a right-banking slope; however, when a camera is mounted on the hood of the car to capture the occupants, the angle is reversed, and the car appears to tilt to the left. That is because the hood camera's tilt is opposite the driver's camera. Therefore, on the first right embankment, George and Blanche appear to be tilted to the left. Then George steers off that first embankment and crosses traffic over to the embankment on the other side of the road, which is sloped to the left. The interior of the car should now tilt to the right. Yet when the hood camera comes back on, the interior of the car is still in the same orientation it was when the car was on the first embankment. The car never tilted in the other direction to match the new sloped embankment.
Poorly devised rear screen projection used for all interior car scenes, especially during the downhill runaway car sequence, where the actors' actions do not match the movement outside of the vehicle.
When Blanche is riding in the back of George's taxi, it's rather obvious the background is a "green screen." Because of this, the street lights ahead of the taxi can be seen moving back and forth right through George's hat and head.
When Mrs Maloney kicks the Shoebridge headstone in the cemetery, you can clearly see indentations from her shoe.
The white mustang blocks exit from the garage at Devane and Black's house, but in a later scene, it is moved back to it only partly blocks the garage exit.