Revealing mistake: Just before the chandelier falls, Col. Mustard quite visibly flinches, even though, realistically, he would have no way of knowing that it was about to crash behind him.
Other mistake: Why on earth would six people from Washington, D.C. be summoned, at night, to a house in New England (as we learn from the opening)? That's a drive of between six and twelve hours depending on where in "New England" it was. Yet none of them remark on the very long drive, or mention staying in hotels, or talk about luggage, or have luggage, or complain about having to stay overnight.
Suggested correction: They are being summoned concerning the blackmail that is happening to them. They have no choice but to go. I don't think any of them were planning on staying the night at Hill House. They were there for dinner and the news about the blackmail. If they have luggage, it is most likely still in their cars.
