The morning of the kite-fighting tournament, Hassan tells Amir about a dream he had: The two of them at Ghargha Lake. However, no one's in the water because apparently there's a monster in there. In Hassan's dream, Amir jumps into the water anyway and Hassan follows. They swim out into the middle of the lake and the people on the shore cheer. The lake is renamed "Lake of Amir and Hassan, Sultans of Kabul." So what does Hassan's dream mean?
It's possible Hassan made up the dream. Amir is very nervous on the morning of the tournament. Hassan could be trying to comfort him through this story. Don't worry, Hassan is saying, a monster isn't waiting for you out in the streets of Kabul. Hassan's truthfulness probably isn't worth too much consideration.
Another fact, however, is worth quite a bit of consideration: later that day, Assef rapes Hassan in the streets of Kabul while Amir stands by and watches. Does this mean Amir is the monster in the lake and that Hassan is horribly wrong? Is Amir's jealousy of Hassan the monster? Or is Assef the monster? Much like the people on the shore, Baba and Rahim Khan cheer for Amir when he wins the kite tournament. Does this mean Baba and Rahim Khan are oblivious of the monster?
This is a complicated little dream. There's probably no one way to interpret it. We can't even say for sure if Hassan is wrong about the monster. If Amir redeems himself later in the novel and overcomes his past, doesn't that mean he and Hassan scare away the monster? That Amir gets rid of the monster inside himself? We can say one thing for sure: even Shmoop's Department of Parapsychology and Dreams had a tough time with this one.