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 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: 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: 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 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: When Charles is looking out of the window, he pushes one slat of the blinds upwards, and then bird watches with his binoculars. When Lydia comes in and makes him jumps, he turns around, and this particular slat falls back downwards, into place. But in the very next shot this same slat is pushed in an upwards position again. When he sits back down again as Lydia leaves, the slat is back down again. (00:27:35)
Revealing mistake: When the charred man is offering Adam a cigarette, you can see the hole in the headrest of the chair where the actor is sticking his head through. (00:31:49)
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)
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 Beetlejuice is using "Zagnut" candy bar as the bait for the fly on his grave, the size of the "Zagnut" is not realistic - the fly should be much smaller than the "Zagnut" bar. (00:36:35)
Other mistake: When Adam and Barbara have their sheets on, trying to scare the mother, they walk out in failure and Lydia takes pictures of the ghosts - polaroid photos fall out (too quickly) and Lydia picks up one which is already developed - they take longer. (00:39:25)
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)
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 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)
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: During the dinner party scene, the positions of the shrimp which hang around the small colourful sushi bowls often change. Sometimes they hang over the bowls, sometimes inside the bowl. This happens with Delia's shrimps especially. (00:48:55)
Continuity mistake: During the scene where the Deitz family and their guests get possessed to sing and dance along to "Day-O," the positions of the black and white napkins, the wine glasses, the cutlery, the wine bottles in the ice-buckets, etc., change many times throughout this completely hilarious scene. (00:50:20)
Continuity mistake: During dinner, Otho is speaking and Delia listens, her hand away from the glass on the table. A shot later she is drinking from it. (00:51:20)
Revealing mistake: When we see that Barbara and Adam are hanging out of the window in order to hide from the Deitz's, it cuts to Beetlejuice yelling "Oh boy. You guys are really a couple of spooksters." In this shot of him shouting, he does not have any white makeup applied to him, nor does he have any of the green patches that run down his neck. In this shot he does not look his usual "dead" state, but looks normal. They obviously forgot to make him look "dead." (00:56:40)
Continuity mistake: When Barbara picks Beetlejuice up from the model town, in one shot his arm is wildly shaking around in fury, but in the next close-up his arm is now tucked in between Barbara's fingers. (00:59:05)
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.