(at around 35 mins) When John Russell first examines the notebook in the attic room, the sticker on the cover says: "C.S.B., January 1909". When he brings Claire Norman to the attic room (at around 38 mins), she picks up the notebook and reads "C.S.B., January FOURTH 1909" off the cover.
(at around 32 mins) When John discovers the door hidden by shelving, when he is removing the shelving and items from in front of the door, after he removes the second shelf suddenly the door is completely uncovered despite there being many more things he would've first had to remove.
(at around 43 mins) John's daughter's ball is red and gray with a white stripe up to the point where it bounces down the stairs the first time. When John takes it to the bridge and when it bounces down the stairs the second time, it is all red with a white stripe.
(at around 50 mins) When the séance resumes for the second time, a camera shot angle shows the metal cone in the center of the table surrounded by the large pieces of paper the medium wrote/scribbled on earlier, however when the camera pans back a moment later when the spirit enters the room from the staircase, the papers are neatly stacked and the cone is off center.
(at around 1 min) In the beginning of the movie when John Russell is shown walking across the road to the phone booth, the road is packed solid with snow. When it shows him reaching the phone booth, in the background you can see that cars have cleared a path with their tires.
(at around 1 min) In the opening scene, when mom and daughter are playing in the snow, there is ample sun and shadowing; when they are pushing the car, and when dad is in the phone booth, it is quite cloudy and overcast.
(at around 11 mins) When John is playing the piano towards the beginning, the above the door next to the fireplace has light behind it. But, when John is called away from the piano, the transom above the door is dark.
When Claire tells John his lease has been canceled, John is looking at her while resting his hand on his head and leaning his elbow on the banister. But in the next shot, his arm is in a different position.
The position of the waitress in the background of the restaurant scene is inconsistent. For example, there's a shot on John where the waitress walks behind him with a tray of drinks. But when the shot cuts back to Claire, she has disappeared. And then later in the same scene, without having shown us that she ever returned to her original position, the waitress than walks behind John again in the same direction, this time holding something else.
(at around 34 mins) After John Russell discovers the secret stairs he gets to a room with an open door. When he looks into the room, the camera moves back and reveals a shadow of a human head disappearing on the left side of the screen. Either this is fully intentional by the filmmaker or it's a shadow of a crew member.
(at around 51 mins) During the second part of the séance when the metal flute object is in the center of the table, the camera's point of view descends the staircase and walks into the room. The shadow of the camera operator is visible on the floor to the left, just after entering the room.
(at around 36 mins) The next scene after John discovers the small child's room and the music box, Claire is listening to music on the reel to reel tape player. There is a large mirror and several small mirrors built into the mantle above the fireplace behind her. As the camera dollies right towards John, you see the arm of a grip pushing the camera in the small right mirror below the single large mirror.
In the final act, the film switches locations between Seattle and Spokane but ignores the 300 mile distance between these cities. Carmichael is earlier shown flying in a private jet from Seattle to Spokane. Later, we are shown John Russell visiting Carmichael in Spokane despite the four hour drive, and an ambulance leaving Carmichael's residence in Spokane and driving past locations in Seattle en route to a hospital.
When John and Claire are in the library looking for information on one of the previous owners of the house, a librarian assists them by taking a microfilm of old newspapers from 1909 out of a drawer. He tells them he'll set it up on the viewer for them, but as they walk over to the viewer (still in the same shot) it is miraculously already loaded and on the viewscreen.
INCORRECTLY REGARDED AS A GOOF: (at around 1 min) There are no telephone poles or wires going to the phone booth in the opening scene. The majority of telephone booths were connected by underground wiring.
(at around 10 mins) When Claire is showing John the piano room the camera moves backwards and it reveals the shadow of the camera. The camera also touches the piece of cloth covering the piano and you can see it moving.
The goof items below may give away important plot points.
(at around 1h 35 mins) When the wheelchair swivels to face Claire just before the chase, Claire mouths "Oh S***". However, the audio tries to pass it off as two separate screams, the second of which occurs after she has already shut her mouth.
(at around 1h 12 mins) When John Russell uncovers the skeletal hand in the well, the metacarpals and phalanges are still connected to one another. If the body had been in the well for 50 years (as the detective says), then the tendons of the hand would have disintegrated, leaving the tiny bones scattered apart the moment the earth around them was disturbed by the shovel.