Continuity mistake: When Nell arrives at Hill House the gate has a padlock on the outside, however when she walks up to the gate to look in, the lock is on the inside so Mr. Dudley can open it. (00:08:15 - 00:09:45)
Continuity mistake: Theo puts on a leather jacket, but in the next shot reflected in the mirror, she puts it on again. (00:18:05)
Continuity mistake: In the scene in which the girls enter the playroom with the revolving floor, you see them, in a shot from the back, step onto the moving floor. In the next shot, from the top, they are back in the entry and step onto the moving floor a second time. (00:21:05)
Continuity mistake: During dinner, Theo starts pouring a glass of wine for Mary. In one shot she has poured about a quarter of the glass full. But in the nest shot the glass is nearly full. (00:23:50)
Continuity mistake: While they're all having their first dinner at Hill House, everyone has a little red wine. The wine levels in Lili Taylor's glass go up and down between different shots. (00:24:35)
Continuity mistake: When Nell opens the ledger, it shows the first page. Two people are crossed out in the ledger. In between the rows which have been crossed out, there are ten rows of recorded people, which aren't crossed out. Nell then puts the ledger on her lap, and is still on the same page. Yet when it shows the page again, there are now only five rows in between the two crossed out ones. (00:55:35)
Continuity mistake: When Nell is looking at the ledger, in one shot she grabs at least one-hundred pages all together, and is about to flip them over to turn to a new page. In the next closeup she is now turning just one single page. (00:55:40)
Continuity mistake: When Nell is searching for Dr. Marrow, and she stops his work on the table, the tape recorded on the table changes position between shots. (01:00:15)
Continuity mistake: When Nell is in the study, the photo album of Crane opens. It then nearly falls so she grabs it. As she grabs it you can see the page has a picture on it, of two people's face very close up. But in the next closeup of the same page, the picture has changed and it is now Crane standing alone in the centre of the picture. (01:02:50)
Continuity mistake: When Nell arrives at Hill House, after Mr. Dudley opens the gate and she drives through, between shots the amount of brown leaves on the ground around the gates increases.
Continuity mistake: As Nell pokes around in the furnace under the fireplace with her iron poker, the bones and ash in it tend to move around, changing their positions many times between shots.
Continuity mistake: When Nell finds the picture album of Hugh Crain and his wife it passes around 3 or 4 pages. But when Nell grabs it, it's about 10 or 20.
Continuity mistake: When Theo and Nell are talking in Theo's bedroom, in one shot Theo removes her black cardigan. In the next shot, you can see in the mirror, that she removes it again.
Continuity mistake: When Nell runs to the Circular Room the second time, she is looking at one of the mirrors. She sees herself pregnant. If you look close, you can see her reaction in the mirror. She brings her hand over her mouth. In the next shot, she does the same thing again.
Continuity mistake: At the first afternoon, Nell is filling out some tests in the Great Hall. We see her put down the same paper twice, one from the ground shot; the other from overhead.
Continuity mistake: When Nell walks to the bookcase, where she was led by the bloody footprints, the vase of peacock feathers on the desk in front of her, change positions between shots.
Continuity mistake: The confetti-like things that are on Theo's hair in the final showdown, disappear in subsequent shots.
Continuity mistake: In the beginning of the movie when the professor's assistant almost gets her eyes injured, Dr. Merrill has the key to open up the lock on the gate, so she can get out to go to the hospital. Later on in the movie, he says they cannot leave until the morning because he doesn't have the key. So it doesn't make sense that he had it earlier but not later.
Continuity mistake: Luke's hair changes length and style throughout the film. It starts off quite long at the back and sides over his ears then after Nell and Theo hear noises on the first night and Luke comes to the door to see what's happening its been cut, coloured and layered then when he's speaking to Liam Neeson a bit later on it's long again.
Answer: Another possibility is the spirits of the children. As long as Hugh Crain was inside the house, the children were trapped inside too. They could have called Nell because they needed her help in being set free.