Continuity mistake: When Matilda makes the chalk write the message on the blackboard, the writing changes. Watch the "Agatha," especially. The handwriting changes and the comma changes length, as well as most of the message changing. Also at the end of the message Matilda "writes" two long lines under it, which cross over. Yet later when Miss Trunchbull flies off the globe you can see there is just one line under the message, not two.