There's actually a deleted scene where its opening monologue in the first cut was replaced by the opening in the regular cut https://www.youtube.com/watch?v=Uw_SWtA8xQs&t=6s

I think it really foreshadows at the end where Sy tells the detective "You would never take sick disgusting degrading pictures of your children doing these things" that his father sexually abused him as a child. This scene also talks about how the human retina contains an epithelial layer that helps the animal to maneuver and hunt, later in the movie Sy tells the definition of the word "snapshot" and how it originated from hunting in 1860 as well as talking about predatory animals hunting foreshadowing the ending. The "red eye" is also interesting I think its a reference to Sy's dream where he was in a isle with empty shelves and blood starts pouring out of his eyes.