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.