Revealing mistake: In the scene when the main character is in the library on the internet, she goes to a couple of websites. When the shot shows the URL up top, it is C:\windows98\mydocuments\etc.html. Instead of actually searching on the web they used a premade html page and accessed it from their computer.
Revealing mistake: When Rachel is racing to save Noah, she is trying to call him on her cell phone. There is a shot of two hands on the steering wheel as the car turns and then a cut to her holding the phone in one hand a split second later while she was talking the entire time, showing that the shot with both hands was a stunt double and not her.
Revealing mistake: After Rachel tumbles down the well, we see her heavy-duty Eveready Commander Flashlight, 12-volt battery and all, bobbing above the surface of the water like a cork. Which is ridiculous. A real 12-volt Commander Flashlight would sink like a rock, because it weighs about 4 pounds. However, the filmmakers needed to explain how Rachel could see at the bottom of a pitch-black well, so they used a lightweight, floating flashlight prop, supposedly providing a light source for the scene.