In Carlo's lover's bedroom we see them leaving in the following order: first Carlo, second Marcus, and third Carlo's lover. But they reach the door in the order: first Carlo, second Carlo's lover, and third Marcus.
When the camera is panning across the record player, when Marcus is playing the 'child's song', the stylus is silver whereas in the next shot when the record is stopped the stylus is completely different (a red one instead).
After the Murder of Amanda Righetti when Proff Giordani is in the Bathroom of her house. He is seen talking to the maid as he has just discovered the message on the wall, He begins to scratch the right side of his head leaving his hair messy. But in the next shot as he is leaving the room we see his hair is back to its normal position.