A metaphor is a comparison that does not use the words "like" or "as."
In one use of a metaphor, Amir likens the past to an object you can bury. An object that is buried is easily forgotten because you are not looking at it all the time: it is lost in a dark place. In saying this, Amir is challenging the cliche that says you can't forget the past:
It’s wrong what they say about the past, I’ve learned, about how you can bury it.
In Afghanistan, the Hazaras are called "load-carrying donkeys," a metaphor that compares them to beasts of burden.This shows how the Hazaras are persecuted by the racist Pashtuns by being reduced to animal status.
In the quote below, Amir compares Hassan to lamb that has to be slain. This is a very traditional metaphor, implying that like a young lamb, Hassan is an innocent whom the more powerful can kill to serve their own needs. This metaphor alludes to Amir's higher position in the social hierarchy than Hassan's, a despised Hazara:
Maybe Hassan was the price I had to pay, the lamb I had to slay, to win Baba.
In the quote below, Amir likens himself to a monster.
There was a monster in the lake. It had grabbed Hassan by the ankles, dragged him to the murky bottom. I was that monster.
Amir uses the metaphor of a monster, conveying how badly he feels about himself. He is consumed with guilt at not confronting Hassan's rapists, which he considers the act of a monster, not a human being. He also uses the metaphor of dragging Hassan to the bottom of a lake to describe how he let him be degraded.