One of the FBI agents opens the door to the helicopter in a high shot and we distinctly see a man 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.
During the runaway car scene 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.
The first time we see Blanche riding in the back of George's taxi it's rather obvious the background is on 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.