Goofs

When Kate gets into the taxicab after the museum, there is a rate listed on the outside of the taxicab. When she gets out, there is a different rate.

In the museum, Kate is wearing pantyhose. When she leaves and is inside the taxicab, she is not.

Outside the museum, Bobbi picks up her glove twice.

The steps outside the Museum alternate between dry and wet.

When Kate writes the second letter, the first one disappears and reappears on the table between shots.

(at around 55 mins) Peter Miller looks in the visor of his Super 8 camera. The format of the visor is 'Cinemascope', which never has been really possible with S8. Later, when the resulting movie is seen, it is in the standard 4/3 format.

After Liz grabs the razor the killer drops in the elevator, she begins to running toward the screaming housekeeper, having left her purse on the floor in front of the elevator. As Liz leaves from the apartment door the housekeeper had gone into, her purse is now over her arm.

Liz actually wears her purse on her right arm throughout the scene. The bag on the floor is left behind by her companion.

After Kate Miller has been attacked with the razor in the elevator, the first closeup of her face shows the blood already dried, which would be impossible if the attack had just taken place.

Although Peter Miller uses a suction-cup audio pickup to overhear the closed-door conversation between Detective Marino and Dr. Elliott, it's apparent in the view from inside Marino's office, as they get up to leave, that the large windowed door does not actually have any glass in it.

Reflections off the door glass can be seen during outside shots, but it was presumably removed for the interior scene in order to keep the waist-level, upward camera angle from revealing all the overhead lights when the door is swung open.

Once the action heightens during the museum sequence, and camera views have switched from tracking shots to Steadicam shots, there is one Steadicam pan in particular (from Kate Miller's point of view) that reveals the on-set lighting equipment at the top of the frame.

The exterior when Kate Miller leaves the museum was filmed outside the Metropolitan Museum of Art in New York, but the interiors are clearly the Philadelphia Museum of Art (made obvious by the museum map on the wall).

Peter Miller claims he's invented a circuit that holds binary numbers and does a carry and that he's never seen it in any of his books. Even in 1980, anyone interested in digital electronics would know that such things were readily available at your local Radio Shack since the late 1970s.