What is the significance of the echo that Adela hears in the days leading up to the trial?
The echo can turn out to mean a couple of things. On one hand, Adela feels that the echo refers to the idea of how the notion of evil is close at hand. Towards some extent, she has unleashed a certain evil out there and the echo is what she sees as a part of this. In a more symbolic sense, the echo is something that overwhelms Adela as the trial becomes closer. The echo is something that wipes out all differentiation, all specifics, all sense of individual distinction because it encompasses all. Adela's echo as it grows overwhelms her memory of what happened in the cave because the echo is all embracing. Inside the echo, just as inside the cave, there is very little demarcation of individual differences. It is only the darkness and all are subsumed by it. As the echo becomes more pronounced in leading up to the trial, it is relieved by Adela recanting on the stand, unable to fully state whether or not Aziz assaulted her in the cave. This echo is representative of not only the fog of memory, but the idea that in such a setting all individual actions are subdued towards something more transcendent and almost higher than that of contingent reality. The echo is all that remains, and individual actions are subservient to it. In the end, when Adela recants, she ends up asserting this.