Miss Trunchbull is not normal. She is dangerously sadistic. She gets away with her behavior because it is so extreme that parents think their children are lying if they try to tell them about what she does.
Some examples of Mrs. Trunchbull's abnormal behavior are as follows:
First, when she is going down a hallway, she does not stop, even if children are in her way. She simply sends children flying in all directions as she clears a path for herself.
Second, Mrs. Trunchbull used to be a hammer thrower in the Olympics. She continues to practice by throwing children. Out on a field one day, she grabs Amanda Thripp by her pigtails and swings her around and around, finally flinging her as far as she can.
Third, she has a tiny closet called the Chokey. Here, she locks children who misbehave. It is lined with broken glass so that a child can't sit or lean against a wall without being cut up. This forces children to stand up perfectly straight the hours they are locked in.
Fourth, when Bruce mistakenly eats a slice of Miss Trunchbull's cake, she makes him eat an entire cake in front of the class. When he does so without getting sick, she hits him over the head with the cake plate.
Fifth, Miss Trunchbull has no interest in educating children and gets angry when she learns that Miss Honey makes learning fun.