(Now we flash back to the incident that leads the Gestapo to Rudy.)
Rudy, Jürgen Schwarz, and Olaf Spiegel are in the doctor's office.
They are ordered to take off their clothes – "They [cup] their genital in their hands and [shiver] like the future" (62.18).
When it comes time to hold out their arms, they have to move their hands.
While they are examined, the nurse tells their teacher, "We are gradually succeeding […] in creating a new future. It will be a new class of physically and mentally advanced Germans. An officer class" (62.24).
(In other words, they are trying to find the best and the brightest – future Nazi leaders and commanders.)
After Rudy's exam, "he manage[s] to perform his first nude Heil Hitler" (62.28).
They hear the doctor and the nurse talking – they want the first boy and the third boy.
Jürgen is definitely the first, but they aren't sure if the third boy is Rudy, or Olaf. Olaf was third in line, but Rudy was third to be examined.
It doesn't matter. The Gestapo will know.
Rudy finally tells Liesel everything, the day after the Gestapo come to his house.
When she lies in bed at night, she can't stop thinking of the moment in the story where Rudy has to move his hand and stand completely naked.