Other mistake: When Julie goes onto the boat to call the police, she sees a collection of newspaper articles and photos stuck to the wall. The photos, however, were taken earlier that same day. Unless they were printed from a colour printer on gloss paper the killer owned in between chasing all of them, there was not enough time to develop them and stick them up. (01:25:15)
Continuity mistake: When Julie gets on Ben's boat, she sees a picture of Helen at the parade from that day. This implies Ben took a picture at the parade, got it developed, then went back and killed Barry and Helen. There's no way.
Continuity mistake: When Helen sees in the mirror that her hair has been cut, she's holding her head with one hand but in the close-up she's holding her head with both hands. (00:57:52)
Continuity mistake: In the iconic scene where Julie screams "what are you waiting for?", she at first faces Barry and Helen then she turns around. In the next shot, she's still facing them and has to turn around again. (01:00:44)
Continuity mistake: When Barry tells Ray to go check if the fisherman is alive, Barry's flashlight keeps changing position from his right hand to his left hand. (00:15:58)