Matilda is so angry at the injustice of being accused of this crime when she didn’t do it that she literally develops a supernatural power—one that allows her to get back at Miss Trunchbull. This suggests that noticing injustices, and wanting to do something about them, can give someone a lot of power (though developing this supernatural power is, of course, far less likely in the real world). For now, though, Matilda’s odd power doesn’t do anything but help her continue her habit of playing tricks on adults; it’s still relatively benign.