Plot hole: Al and Peg are upstairs with the killer. Both of them are screaming, but downstairs, you can't hear anything. Everyone is sitting around talking. It's not until Al and Peg scream again that everyone runs upstairs. And you can tell the screams were "on cue" also.
Factual error: In the game show near the end, when Marcy and Steve come out as Al and Peggy. When the real Al and Peggy win the car, because they used Marcy and Steve's names, the car would have never gone to the real Al and Peggy. In reality, it would have gone to Steve and Marcy because it was won under their names. Al and Peggy would not have been able to keep the car. In fact Al and Peggy would not have been allowed to be on the show at all using someone else's name.