how dose amir half-payfully test hassan's loyalty?

Amir decides to "toy" with Hassan when he asks him whether or not Amir would he ever he ever lie to him. Amir asks him "Would you?" and Hassan responds he would rather eat dirt. Amir asks him whether or not he would eat dirt if he told him to. There is a moment when Amir and Hassan just look at each other. It is at this moment that Amir says that " Hassan's face changed.... I was looking at two faces, the one I knew, the one that was my first memory, and another, a second face, this one lurking just beneath the surface." page 54. This "second face" that Amir sees, shows him that Hassan is not as simple as he thinks he is but that he is capable of deeper thought and knows when he is not treating him right.