Tanya got sent to the headmaster's office by her gym teacher when she refused to take part in gym class, and she and Peregrine were so badly-behaved to him that he faints.
The following day a new barber moved into Saucy-by-Sea and he told Tanya and Peregrine to come and get their hair cut at his shop the next day. However, when they arrived it was revealed that the barber was actually going to snip out the parts of their tongues that made them so cheeky.
When Tanya returned to school the following Monday, she was no longer badly-behaved, and her tongue was considerably shorter . . .