One night, Nick makes "the great blackbird discovery," which provides him with an opportunity to make more mischief at school. From a TV show, he learns that red-wing blackbirds let out this high-pitched chirp whenever there's danger around. Because of the way the sound travels, the red-wing blackbird's predators can't tell where it's coming from.
This gives Nick what he thinks is the great idea of making a high-pitched noise in class whose source won't be detected by his teacher Mrs. Avery. The next day, he tries it out, and, sure enough, it seems to work. When Nick makes the high-pitched noise, Mrs. Avery looks up from her book and, because she can't tell who's making the noise, she tells the whole class to "Shhh!"
Soon after, Nick repeats the trick, only this time a little louder. Initially, Mrs. Avery pretends not to hear it, but fifteen seconds later, she walks to the back of the classroom. As she does so, Nick lets out his third and final chirp, this one louder and more annoying than the other two.
Mrs. Avery pounces on Janet Fisk, telling her to stop this instant. Janet immediately protests her innocence. Thankfully, Mrs. Avery realizes that she's made a mistake and apologizes. She also tells the class that someone is asking for big trouble.