The Magic of Illusion

The Usual Suspects kept it old school—shooting on 35 mm film—because it had to. It was 1995: no one was shooting movies digitally yet. (Source)

Some cool film techniques are on display in this movie: when Verbal tells the legend of Keyser Söze's origin, we see the story play out in a dream-like, sepia haze—the style of filming lets us know that we're seeing a story, not necessarily something that really happened.

To highlight the surreal nature of it all, when we glimpse Keyser Söze in that part of the movie, he ends up looking nothing like the real Keyser Söze—Verbal Kint—whose identity is revealed at the end.

Also, in the final sequence, as Kujan realizes the truth about Verbal, the movie intercuts scenes of Verbal-as-Söze shooting his fellow criminals at the dock, along with voiceover clips of things Verbal said earlier in the movie. As Kujan notices different clues on the bulletin board, we hear Verbal's voice saying things from earlier in the movie—statements that Kujan is realizing were lies.