In the opening credits there are two cars in the driveway. A brown car with a white top and a Gray car behind it in the drive way. We are still in the beginning credits when David Brown leaves the house. He gets in the brown/White car the other one is not there. After the Police arrive both cars are in the driveway again but opposite of the start of the movie.
When the Police first arrive David refers to Patty as his sister-in-law, but later the same cop seems very surprised Patty and Linda were sisters.