Brother Leon is asking David Caroni if he's surprised he got an F on the test.
David is surprised. The lowest grade he's ever made is a B-. His scores are always astronomical. An F will screw everything up.
Leon is saying that he's rather shocked himself, considering David's usually excellent grades.
Leon explains that the test, which was just pass or fail, was actually rather hard. At first, Leon thought David passed. In some ways he got things right, but in other ways….
Now Leon is telling David that people don't always realize it, but "teachers are human too" (16.13). Even teachers can make mistakes, especially on tests like these, where there are multiple answers to the questions.
David isn't really sure where Leon is headed with all this.
Soon, Leon turns the topic to the chocolate sale. He congratulates David on his sales, but says that some people aren't such good examples.
Like Jerry Renault.
Aha. Now David gets it.
His head starts hurting, and he can feel a migraine lurking. He starts feeling nauseas.
Very gradually Leon gets to the point. He wants to know why Jerry isn't selling the chocolates.
David considers not telling Leon what's up with Jerry, but then he imagines a future of Fs before him.
So he spills the beans – Renault isn't selling chocolates because The Vigils told him not to. He has to refuse the chocolates for ten days.
Leon is relieved. Tomorrow is the eleventh day of the chocolate sale.
Leon tells David he can go now.
David manages to ask him about the F.
Oh, that, Leon says. He tells David to check with him at the end of the semester, after Leon's had time to review the test again.
Now David is relieved, but he feels horrible, mostly because "he had allowed Brother Leon to blackmail him." He wonders, "If teachers did this kind of thing, what kind of world could it be?" (16.45).
Brother Leon is saying that David still might get an F, though.
David has the terrible realization that life is an awful thing, and that you can't count on others, or even count on yourself.
He runs out, afraid if he stays a moment longer he'll throw-up.