(76:13) In the English dubbed version, the Latin sentence cited by Prof. Milius is full of mistakes and thus virtually unintelligible ("Quandum ubique, quandum semper, quandum ad omnibus creditur est."). The line as intended by the author can, however, be heard in the Italian version: "Quoddam semper, quoddam ubique, quoddam ab omnibus creditum est."
The morning Suzy arrives at the school, Miss Tanner tells Suzy that they were expecting her the night before. Suzy replies that she had arrived at the school the night before, at 10 o'clock, but the door was locked. However on her way up the staircase, when Madame Blanc is explaining to the officers about the murdered girl's expulsion, Suzy interrupts to say she saw a girl leaving when she arrived at 11.
When Suzy is talking with the old Psychiatrist at the Convention Centre and the camera slowly zooms in on the windows behind them and focuses on their reflections we can also see Dario Argento on the left side of the frame in a white t-shirt observing the scene and looking backing and forth. (More noticeable in the Blu-ray release.)
During the opening cab ride to the school, Suzy asks the cab driver "has it been raining this hard for long?" As the driver turns back towards her just before responds you can see just outside the driver's window (on the left side of the shot) a pillar-like rotating piece of lighting equipment that is clearly the source of the red and yellow strobe lighting during the entire scene.
Dario Argento's face can be seen reflected on the taxi's glass partition in the opening sequence. Assumed by many people to have been a mistake coming from a rushed shoot, Argento has gone on record to say it was intentional.