Nina Petrovna is trying to root out who defaced (or de-nosed) the statue of Stalin.
She makes each student get out a piece of paper, and write down the names of suspicious kids who might have done something like this.
Oh, wait. Since one student, Zina Krivko, is a bit confused, the teacher changes the rules. The students should write down the names of those they are certain did not do it.
But, there's a catch (we're starting to see that in this society there invariably is): if any name on the list turns out to be wrong, the student who made the list will end up being suspected herself.
And, the rules change once again after Zina expresses uncertainty about not knowing whom to trust. Now, the students should write down the names of those they are not sure are reliable.
Yep, this is getting out of hand.
When Sasha does not immediately write a name, Nina Petrovna makes it very clear she would like for him to write down Vovka. She even wants Vovka to write down his own name, and basically identify himself as a criminal. Ditto for Four-Eyes.
Well, Vovka doesn't like this at all, and just as he's standing up to maybe do something rash (like give Nina a thrashing), they are all summoned to the cafeteria by orders of the Chief.