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 driveway. As the credits continue, David Brown leaves the house and gets into the brown-and-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 Patti as his sister-in-law, but later the same cop seems very surprised that Patti and Linda were sisters.