Revealing mistake: When Natalie is in the old building and she is looking around, she opens the door and Parker's dead body falls out onto the floor. When it cuts to a close up of his body, you can clearly see the side of his neck pulsating although he is dead. (01:19:50)
Revealing mistake: When the killer calls Parker, when we see the phone it's not showing details from caller ID, it's just showing the address book.
Revealing mistake: When Natalie discovers Tosh's body, a close up shows Tosh visibly blink her eyes.
Revealing mistake: In the chase sequence, we get a shot of who is supposed to be "Brenda" driving, but we see the eye of a man, not a woman. Brenda doesn't have bushy eyebrows, and her eyes are a different shade of blue. (01:20:05 - 01:24:20)
Chosen answer: She is saying "I'm not stuck, he is!" which was what the caller was saying when she was disconnected.