Symbolism, Imagery, Allegory
One day, when he's out chilling in the desert, Santiago watches a couple of hawks flying in the sky. Suddenly though, they reveal much more to him than what you could learn on The Discovery Channel. In fact, they reveal a whole secret message:
Suddenly, one of the hawks made a flashing dive through the sky, attacking the other. As it did so, a sudden, fleeting image came to the boy: an army, with its swords at the ready, riding into the oasis. (2.304)
Oops. That's not good. The hawks, in their own violence, reveal the violence that is about to come to the oasis. In a way, you could even say they're a symbol for symbols: they show us that the desert, and in fact the whole world, is always trying to reveal itself to Santiago and other dreamers.