The opening sequence uses a lot of transitions and close up shots. The close up shots reduce the viewers sense of what is happening or rather who and where something is happening. The audio that goes with the sequence heightens the effect as the scratchy sounds as well as the flashing transitions which confuse the viewer. We believe this makes the sequence highly effective and it doesn't give too much away about the story.
The thriller conventions used in Se7en are: Darkness, blood, miss-information, mystery, strange music, Strobes, scratchy sounds, distortion of text, quick camera changes and needles.