Revealing mistake: In the first scene where we are introduced to Alex Forrest at the bar during the cocktail party, she is almost always smoking cigarettes that are not lit. She continually dashes out ashes that aren't there and there is never any smoke coming from the cigarettes.
Deliberate mistake: When Michael Douglas pretends to be hurt in the field, Glenn Close says, "You bastard," and her hair is not in the sunlight. In the very next shot it is. (00:27:00)
Continuity mistake: When the phone rings as Beth paints, Beth puts her roller in the tray and goes to answer the phone. When she returns the roller is in a different position than it was before.
Answer: So her parents (especially her father) would go through hell, not knowing where she was or if she was safe.
Brian Katcher