In Chapter 5, in order to pass the selection process, Elie is advised to move about so that he will have "a little color" before the selection. He should also be careful not to walk slowly, in fact, he should run "as if the devil were after (him)". As he is running, he should not look at the SS; he look straight in front of him. And above all, he should not be afraid.
The head of Elie's block is a longtime veteran of the camps - he "had never been outside concentration camps since 1933...he had already been through all the slaughterhouses, all the factories of death". A few moments before the selection process begins, he stands in the midst of the prisoners and tells them what the process will entail and how they might best ensure their survival. He says that they must get completely undressed and "go one by one before the SS doctors". It is imperative that they appear as healthy as possible, and that the doctors not be able to record their numbers as they pass by.
For this particular selection, three SS officers stand around "the notorious Dr. Mengele", known as "the angel of death". As the prisoners run by one by one, Mengele takes stock of them and occasionally writes a number down. When it is Elie's turn, he runs as fast as he can without looking back. He is judged to be fit enough to continue to live, or else he runs so fast that the SS cannot see his number; either way, Elie survives the selection (Chapter 5).