The rich imagery with which Steinbeck begins Section 6, the powerful conclusion, evokes the novella’s dominant themes. After killing Curley’s wife, Lennie returns to the clearing that he and George designate, at the beginning of the book, as a meeting place should they be separated or run into trouble. Here Steinbeck describes much of the natural splendor as revealed in the opening pages of the work. The images of the valley and mountains, the climbing sun, and the shaded pool suggest a natural paradise, like the Garden of Eden. The reader’s sense of return to a paradise of security and comfort is furthered by the knowledge that George and Lennie have claimed this space as a safe haven, a place to which they can return in times of trouble.
This paradise, however, is lost. The snake sliding through the water recalls the conclusion of the story of Eden, in which the forces of evil appeared as a snake and caused humanity’s fall from grace. Steinbeck is a master at symbolism, and here he skillfully employs both the snake and heron to emphasize the predatory nature of the world and to foreshadow Lennie’s imminent death. The snake that glides through the waters without harm at the beginning of the story is now unsuspectingly snatched from the world of the living. Soon, Lennie’s life will be taken from him, and he will be just as unsuspecting as the snake when the final blow is delivered.
This is from...
http://www.sparknotes.com/lit/micemen/quotes.html#explanation5
You should so, like, go there and like read stuff from it, right, 'cos it's just got like so many more of stuff like this on it and it's dead brilliant like isn't it?