Continuity mistake: When Mrs. Waterhouse walks into the livingroom and greets her three babies, there is a large area rug in front of the coffee table. However, as the babies fly towards her in the wide shot facing her, that area rug is gone! (00:22:55 - 00:23:50)
Continuity mistake: At Mrs. Waterhouse's home, the large potted tree, beside the doorway with the bouncing baby, is visible in consecutive shots and the leaves' position obviously differs in those shots. (00:22:55)
Continuity mistake: After Mrs. Waterhouse says good morning to her children, in the wide shot she walks to the coffee table to get her mail. In the next close-up, a couple of things disappear from the table, as well as the pillow on the floor, which leans against the couch behind the table. (00:23:00)
Revealing mistake: As the three babies fly towards Mrs. Waterhouse, when they land on her it is blatantly apparent that they're merely three dolls in this shot. She actually grips two from behind and the center doll is attached to her as she moves backwards. Also, in the shot facing the babies the center baby is in the bouncer seat with the rod attachment overhead, yet, in the shot facing Mrs. Waterhouse the rod attachment is gone. (00:23:50)
Continuity mistake: After Frank 'bumps into' the hearse leading the funeral procession, he sees Ray's ghost running up the street towards him. In Frank's front close-up as he raises his arms in shock, the whicker baskets in front of the pet shop are on his left. As Frank hits the ground the baskets are beside him and they are arranged quite differently. (00:26:15)
Revealing mistake: At the Excalibur Restaurant, when Ray's ghost gets angry at Frank he knocks over a wine glass with his hand. When the wine glass starts to tip over, the cloth under it moves and lifts up a bit to obviously tilt the glass towards Frank. (00:36:40)
Continuity mistake: During the dinner with Lucy at the restaurant, Ray's ghost knocks over the wine glass and the wine visibly spills onto Frank's vest, yet, the vest is dry in the following shots. (00:36:40)
Continuity mistake: During the dinner with Lucy, Frank goes to the lavatory to dry his pants and when he pulls on the paper towels more than a foot is left hanging out the bottom of the dispenser. However, in the following shots it's either nothing or a some of it sticking out of the dispenser. (00:37:00)
Revealing mistake: The scar near Agent Dammers's left eye changes shape and position throughout the film. (00:41:15 - 01:35:25)
Continuity mistake: At the police station, when Dammers tells Lucy about the day that Debra died, there is a shot of the utility knife in Frank's toolbox and the initials F.B. are written in white on the knife. Later, when Lucy finds Frank's utility knife in Mrs. Bradley's bedroom, the initials are written differently. (00:44:30 - 01:05:50)
Continuity mistake: At the police station, the filing cabinet beside Lucy is visible in the wide shot, just before Dammers says, "Debra's corpse had the number thirteen carved into its forehead." Then, in Lucy's close-up different things are on top of the filing cabinet. (00:46:10)
Continuity mistake: At the police station, when Agent Dammers sticks his badge in front of Sheriff Perry's face, the position of the badge in his hand differs in the shots facing Perry and the close-ups of the badge. (00:56:10)
Visible crew/equipment: When Frank is in the freezer in the hospital laboratory, as Lucy and Agent Dammers fight over the door latch, the brief reflection of a crew member wearing red is visible in the large polished stainless steel hinge on the door. (01:14:10)
Continuity mistake: The red marks on Frank's neck change in consecutive shots from the time he receives the injury. (01:29:30)
Continuity mistake: After Frank takes the urn from Lucy, he reaches the bench near the chapel and a wood chair lies on its side beside the bench. After Dammers catches the urn, that chair is now upright behind Frank. (01:34:55 - 01:35:50)
Continuity mistake: When Frank reaches the chapel he places the urn down and there are scattered pieces of wood hanging over the edge of the bench. After Frank breaks through some of the wood on the chapel door he causes the pedestal to fall over on the bench and the wood is gone. (01:34:55)
Continuity mistake: When Frank hacks away at the door of the chapel, the broken wood at the openings differ in the close-up of Frank's face through the door and the following shots. (01:35:00)
Visible crew/equipment: Outside the chapel, when Frank backs into the pedestal the statue begins to topple over. In the shot facing up, as the pedestal falls and Frank puts his arms out to catch the statue, the wires used in this stunt are perfectly visible. (01:35:05)
Continuity mistake: Frank catches the statue, that he accidentally knocks over near the chapel. The way he catches it is completely different in the first shot facing up and the next close-up. (01:35:05)
Continuity mistake: In the sanatorium, after Frank accidentally knocks over the statue outside the chapel, the pedestal falls onto the bench sending the urn flying above. In the overhead wide shot the urn flies upside down as it reaches the window, yet, in the next close-up the urn is right side up as it comes through the window. (01:35:10)
Chosen answer: For the most part, the actors playing the ghosts were shot separately on blue-screens, and then comped into the scenes. (By removing the blue background through a process called "color keying", and placing them over the scenes) They were simply given a blueish glow and made semi-translucent to complete the effect. It was pretty cutting edge back in the 90's, but nowadays, it'd be very easy to make the exact same effect using a simple program like Adobe After Effects.
TedStixon