[crabapple]

Oh, well, this is just the opening monologue you're talking about.

According to the director commentary, the studio wanted it added (at the last minute, basically) because they felt the film would be too confusing without a basic explanation at the beginning to frame the action.

In a sense, it does ruin the totality of the story's mystery; but a good truckload of stuff isn't revealed that you still get to discover as the story unfolds. Personally, I liked the monologue and found it rather creepy.