It's worth noticing that while Matilda says she's going to play pranks on both her parents whenever they behave badly to her, the pranks we read about in this book mostly target her father. The ghost-parrot scares everybody, of course, but it makes Mr. Wormwood look the worst, not Mrs. Wormwood. It's Mr. Wormwood who ends up with a hat stuck to his head, and Mr. Wormwood who gets his hair dyed the wrong color.