Continuity mistake: When Delia spray paints the word “mauve” on the wall, between shots it is apparent that the script of the word changes. One example would be that in the first shot the tops of the letter “M” are pointed, like triangle tips, but in the next they are more rounder. The writing also moves lower on the wall. (00:15:50)
Continuity mistake: When Otho is going through the house suggesting changes he is wearing white sneakers in one room and red ones in the next. (00:16:25)
Revealing mistake: Adam and Barbara aren't supposed to have reflections, but when they enter the recreation of their home (just before they meet Juno), their reflections are shown perfectly in the glass display case that holds Delia's sculptures, behind them. (00:32:55)
Revealing mistake: When Barbara and Adam are digging up Beetlejuice's grave, you can see that a piece of cardboard states "FRAGILE" or something in small print which is proportional to Barbara and Adam at that time. However, the lettering should be ten times larger if the cardboard was proportional to the actual model. (00:44:35)
Continuity mistake: When the Deetz family first check out the house, Otho shakes up a can of spray paint, takes off the cap, and hands it to Delia. When it cuts to the next shot, you can see Delia take off the can's cap again. (00:15:30)
Visible crew/equipment: When Adam, Barbara and Juno ascend a staircase, talking about how Adam and Barbara should start more simply if they want to scare the Deitz family out of their home, there are two tape markers - a yellow and a blue one, very clearly on one of the steps. (00:34:35)
Revealing mistake: When Barbara is moving the little plastic horse in front of the mirror to prove that she's invisible, the "reflection" of the horse is not synchronised with the actual horse. (00:09:10)
Revealing mistake: In the scene where Barbara is showing Adam that they have no reflections by moving the horse in front of the mirror, Adam's reflection can be seen in the windows in the background. (00:09:10)
Continuity mistake: In the part where Barbara and Adam are asked to draw a door on a wall in case of an emergency, there is already a chalk outline of where a door would be. (00:25:55)
Continuity mistake: After drawing the chalk door, Adam knocks on it three times, and then it opens. Adam then sets down the "Handbook for the Recently Deceased" and puts the piece of chalk down next to it. But later, when Lydia sneaks up into the attic, she finds the handbook, now with the piece of chalk sitting on top of the book. (00:26:55 - 00:30:10)
Continuity mistake: When Otho is calling the spirits of Barbara and Adam to return we see Barbara first, suspended above the table in her wedding gown. She "ages" so rapidly during Otho's chant that her skin shrivels and her feet curl up, causing one of her shoes to fall off onto the table. A few minutes later we see a long shot of both Barbara and Adam suspended above the table, but her shoes are both on and there is nothing on the table. (01:13:30)
Continuity mistake: When Adam creates the door to gain access to the spiritual world, he draws the outline and door knob quite visibly with chalk. Yet when the door is closing after they have gone through it, though you can still see the outline of the door, the door knob has mysteriously vanished. (00:26:15)
Continuity mistake: When the fly lands in the cemetery, the ground is some sort of spiked rubber. When the camera is flying in, we see the cemetery is actually dirt and sand glued to the board.
Revealing mistake: When Adam, who should have no reflection, walks out of the door to go retrace his steps, he is really clearly reflected in the big glass panel in the door. Then after Barbara pulls Adam from the SandWorm land, they walk back into the house through the same doors, and are both reflected in the glass panels of the door. So much for ghosts... (00:08:50)
Visible crew/equipment: When Barbara tries to leave the house and falls into the sandworm's world you can clearly see her knee pads. (00:19:00)
Visible crew/equipment: When Otho is doing the Seance, Adam and Barbara appear in their wedding clothes and then float above the table. When Lydia releases Beetlejuice, everyone gets up and leaves the table, and in this wideshot the black wires that Adam and Barbara are suspended from are visible. (01:15:25)
Continuity mistake: When Beetlejuice is in the waiting room at the end of the movie, he speaks to one man with a shrunken head, who does not reply. He then turns to the voodoo man sitting to his right, and he notices that this man has the a lower ticket number, so he steals this mans ticket and then throws his own ticket into the voodoo mans lap. But in the next shot the ticket is not in the voodoo mans lap, but it is on the seat beside his left leg. (01:24:15)
Continuity mistake: When Adam and Barbara try to scare the new residents out of their house, Barbara holds up Adam's head by the hair. He has glasses on and they are up on his nose where one would wear glasses. However, the next shot is a close-up of the head, and the glasses are down on the end of his nose. (00:16:50)
Visible crew/equipment: Barbara shows Adam their lack of reflections, then points out the book entitled "Handbook for the Recently Deceased" and its publisher. At the very start of the next shot in their bedroom, we can see the reflection of the moving boom pole/mic on the window above the bed. (00:10:10)
Continuity mistake: The distance between the picture hanging on the wall and the light switch wire often changes through the movie. Look at the distance between the two when Adam walks past to throw the spider out of the window. When Barbara pokes her head into the room in the following shot to give Adam his present, the picture now hangs right beside the light switch wire. (00:02:35)
Answer: They died by drowning. Jane's daughter even tells Lydia when she asks what happened. Although Adam and Barbara should have been completely wet for the whole movie, Tim Burton decided to keep Alec and Geena dry as he felt that keeping them wet the entire time would be an uncomfortable experience for both of them.