Continuity mistake: In the scene where Big Momma's gentleman caller comes to the door, Martin Lawrence runs over to the door and stands directly in front of it with both of his hands up gripping his gun. This can be seen in the shot when we see into the house through the window on the door. In the very next shot both of his hands are down.
Continuity mistake: When Big Momma (Martin Lawrence) is in the place where Nolan supposedly teaches them to defend themselves. When Nolan is looking at Gertrude, you can clearly see a young face, with no wrinkles. Then when she is laying down on the floor, there is a very old face. They used a double for the scene in which she is hit.
Continuity mistake: When Big Momma wakes up to find that his face is peeling off and Shari knocks on the door, Big Momma goes out the window and his whole outfit comes off. He is completely dressed in a T shirt, sweats and tennis shoes. Why would he have clothes on under Big Momma's outfit, it would be too hot.
Other mistake: In the scene where they surprise Big Momma for her birthday, Nolan takes the gun from Malcolm (he says give it to me, you ain't supposed to have that, etc. then says I'm gonna go secure the perimeter when he gets the gun) . They show the gun and their hands up close. It is loaded, the safety is off, it is cocked and Malcolm has his finger on the trigger. Nolan is pressing Malcolm's fingers. If he had really been fighting for the gun the way it seems, the gun would have gone off.