Continuity mistake: Julie goes to the mirror and wipes away some of the condensation from it, still leaving some condensation on it. However when Julie walks away from the mirror, the whole mirror is suddenly clean. (00:47:00)
Continuity mistake: Julie leaves the classroom and walks along, talking to Will, and she has two bags on one shoulder. In nearly every shot the bagstraps change position. (00:04:00)
Continuity mistake: The spots of blood on Titus's chin differ and disappear after he gets stabbed in the hand. (00:52:05)
Continuity mistake: When Ben falls in the grave his eyes are closed, then the camera cuts and the first or second time it cuts and you can see his eyes sort of open.
Continuity mistake: When Julie is in the confessional, a tear slowly trickles down the center of her left cheek. We then cut to a side shot and the tear has moved next to her nose. (00:02:50)
Continuity mistake: Before Julie gets her knife and cuts Will with it, the camera zooms out and you can see her go for the knife and not get it, so they make you think she actually is supposed to go for it the second time. (01:24:00)
Continuity mistake: When the four are walking to the hotel, as they walk under the outdoor archway, Tyrell's glasses move from up on his head, to on his nose, to back up on his head between shots. (00:25:50)
Answer: I believe it was supposed to be a surprise plot twist, I don't remember there being any indication that Will was setting them up.