In the pre-credit "slasher movie" sequence, the shadowed reflections of both the "slasher" (intended or, at least, credible) and the camera operator and his Steadicam (unintended) can be seen in the tile wall to the right of the showering girl. Perhaps the reason the girl was hired, as explained to John T's character in the projection room by the film's producer, was thought to be a sufficient distraction so as to preclude a retake.
As the Burke character (John Lithgow) speaks to his contact from the "secure" public phone in downtown Philadelphia, the same maroon MGB convertible is seen directly across in the same metered space throughout the conversations that take place on different days.
The sound mixer for the slasher movie mutes all of the sounds except the scream of the girl in the shower, in order to prove that it's really her voice. In fact, what he proves is that she's been dubbed: if it were really sound from the location he would not have been able to eliminate the shower or its curtain being pulled aside, as the microphone would have picked them up too.