You know, way back in the eighties, I caught a college showing of PSYCHO. As the movie neared its conclusion, I was shocked to realize that several members of the audience didn't realize (52-YEAR-OLD SPOILER ALERT!) that Norman was the killer and that there wasn't really a crazy knife-wielding old lady in the basement . . . .
So I guess you can't always assume that everybody is familiar with even the most classic movies!