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)
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)
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.
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)
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)
Continuity mistake: When Charles is sitting by the window, he picks up a book and starts to look through. After he mutters "ah, birdies," he turns to the next page, and on the left page there is just a small paragraph of text at the bottom of the page. Yet in the next wide shot there is now another big paragraph of text on the centre of the page. It is meant to be the same page, yet it obviously is not. (00:27:25)
Continuity mistake: After Adam has drawn the chalk door on the wall, he walks forward and closes the “Handbook for the Recently Deceased.” In the next shot, as he knocks on the chalk door three times, the handbook is now open. In the next shot as he steps back, the handbook is now closed again. (00:26:20)
Continuity mistake: In the wedding scene at the end when Barbara comes crashing through the ceiling on the sandworm, Beetlejuice looks up at the ceiling, which is still intact, and screams - a split second later Barbara actually crashes through and the sandworm devours Beetlejuice. (01:20:45)
Continuity mistake: During the dinner party, in one shot from behind we see Otho has very little wine in his glass, but in the following shot of him from in front, his glass is now nearly full. Nobody refilled it between the shots. (00:48:55)
Continuity mistake: When Alec Baldwin tries to leave the house and ends up in the sand world for a few seconds, his wife says that he was gone for two hours when he gets back. When the wife is sent to the sand world for a minute at the end of the film, she returns to the house only a few minutes later. (00:09:00 - 01:21:00)
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 the house starts shaking, we see a shot of Adam roll over in bed with a blanket wrapped around his body. In the next shot the blanket is in a totally different position around him. (00:12:45)
Continuity mistake: When Barbara tears the top of the wrapping paper off of the present (tube of wallpaper) Adam bought her, in following shots the way the paper is torn and the way it hangs, changes. In the very next wide shot the whole of the wrapping paper is suddenly off of the tube of wallpaper, without enough time given for Barbara to have pulled it off. In following shots Adam and Barbara kiss and cuddle on the couch, and in one shot you can see that the wrapping paper had reappeared, and is still wrapped around the tube. (00:03:00)
Continuity mistake: Adam draws the chalk door on the wall, and next to the door there is a long wooden pole. But in the next shot the wooden pole has now moved along, to cover up the right chalk door-line. (00:26:00)
Continuity mistake: When Lydia dances at the end, the two times we see the top of her head, her hair is parted differently. (01:23:20)
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.