What does eliezer repeatedly say about the many terrible things that he has seen?

This question is from "Night", which is a biography. He uses the repetition to make himself not to forget the horrible experiences he saw in the past. He lists at least five things that he will never forget:

1) - the night he saw deaths.

2) - First night in camp

3) - smoke

4) - Faces of children

5) - flames.