Serious errors - SPOLIERS
This movie had some of the dumbest mistakes I have ever seen in a movie. One has to overlook these things in order to enjoy an Argento movie, granted, but this movie goes too far, even for him.
The characters constantly refer to Aura's anorexia, but we see her throwing up right after she eats. Surely she has bulimia, not anorexia. That said, she also starves herself. So does she have both? Is that even possible?
Secondly, I find it hard to believe that the cops wouldn't have found out pretty quickly that there was a clear connection between all the victims - it wasn't exactly a huge secret that these people had once worked together and the cops would've known that almost immediately after the second murder.
It also made me chuckle that Rydell's character was so determined to catch the killer himself instead of just giving the information he had to the police. We were given no reason for Rydell's supposed altruism at all.
Nor was it explained why this 20-something newspaper cartoonist (or whatever he was) lived in a house with a huge garden backing onto a lake - how does he afford that?
Then there was the scene where he and Aura returned to her parents' house THE DAY AFTER two murders took place there and there were no cops anywhere, just a measly 'do not cross' tape across the porch. That place would have been crawling with cops; crime scene workers, forensic people, criminal psychologists...
Perhaps the worst bit was immediately after they escaped the mental institution where Aura was being held. Rydell saw two of the dead bodies right before they left ("you did it, you did it..."). In the next scene they're watching the news back at his place and there's a report about the murders and he's like "Look, there were murders at the hospital", like he didn't already know. What's with that?!? I have heard that there are lots of scenes cut from some versions of this movie, but I can't imagine how that could possibly be explained.
Besides that, the script was sooooo bad. The dialogue was so clumsy and obvious. One has to wonder what the hell Frederick Forrest, Brad Dourif and Piper Laurie were thinking when they signed up for this movie...