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)
Revealing mistake: In the scene when Beetlejuice is getting married, you can see the priest in the fireplace after he supposedly burns up. (01:21:15)
Revealing mistake: After the scene where Barbara's fingers catch fire, the Maitland's walk down the hall (and Barbara says "I'll make us some coffee), and in the picture hanging on the wall to the left of the screen, we see their reflections. They shouldn't have reflections, as proved by the mirror. (00:08:30)
Revealing mistake: When Beetlejuice rises from the grave, and then flies after Adam and Barbra, for a split second, you can see a wire over one of his shoulders, but it is pretty hard to spot. (00:45:05)
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)
Revealing mistake: When Delia and Otho go upstairs, Delia takes her can of spray and writes the word "mauve" on one of the walls. The faded marks of mauve spray paint are quite evident on the wall as she sprays the word, which reveals that this was not the first take of the scene. (00:16:00)
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)
Continuity mistake: When Adam and Barbara are sleeping, they awake to a sudden commence of the whole house shaking. There is one close shot of the items on the mantelpiece. Watch the items. There are reels of cotton on the centre of the mantel which vanish between shots, and in the wide shot a book has appeared in front of one of the photo frames, which wasn't there beforehand. (00:12:50)
Other mistake: If the dead characters all are continuously displaying how they died, Adam and Barbara should constantly look wet, but they don't.
Revealing mistake: At the end when Lydia is being lifted into the air during the "Senora" song, if you look very carefully, you can see the wire lifting her up.
Continuity mistake: At the end when Beetlejuice is sitting next to the witch doctor he throws the number on his lap. When the doctor picks it up it's beside him on the chair.
Revealing mistake: At the start, after the car veers away from hitting the dog and comes to rest teetering on the edge of the bridge, you can see the quick release wire cable that was used to secure the car to the bridge. It's also very visible when the car is sinking into the water. (00:07:50)
Revealing mistake: At the end, as Beetlejuice's head shrinks, the collar has a line around it, showing where the two images were superimposed.
Continuity mistake: When the Deitz family and their guests are eating, the bowls of shrimp are sitting on small mats. Delia and Charles's mats often change from black to grey colour, at random through the whole dinner scene. (00:48:45)
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.