Dana's beautiful eyes, made even more beautiful by her glasses, are her unique feature: "With two eyes she was pretty. With four eyes she was beautiful" (11.1). It stands to reason that if she was covered with eyes, she'd be even more beautiful, but this isn't the case—instead, poor Dana is "covered with mosquito bites" (11.2).
Dana complains to Mrs. Jewls that she can't do arithmetic because she's too itchy. This prompts the rest of the class to complain about other things: too tired, too hungry, too stupid.
Mrs. Jewls announces that arithmetic is the "best known cure for an itch" (11.16), and she asks Dana how many mosquito bites she has.
Dana estimates that she has over a hundred bites, but her itch keeps moving from bite to bite. "The itch just never stays in the same place" (11.17), she says.
Mrs. Jewls once again recommends arithmetic. "Mosquito bites itch, not numbers" (11.20), she reminds Dana—and then she proposes turning Dana's mosquito bites into numbers. Maybe Mrs. Jewls knows more magic than Mrs. Gorf?
Mrs. Jewls starts quizzing the class, using mosquito bites in all the math problems. But Dana still itches. Finally Dana starts counting her own bites. When she adds all of her bites together, she gets a grand total of one hundred and twenty-four. No wonder she was going nuts.
Once Dana counts all of her bites, they don't itch anymore.
The rest of the students wonder if arithmetic can also fix their complaints. "I'm still stupid" (11.44), Todd remarks.
Dana is grateful that her bites were turned into numbers instead of letters, because she just can't remember how to spell mosquito.