Find the scene where Dr. Abigail Chase is in her office and she receives the small, red box containing the last button she needed. When she removes the gold string, it's small and she tosses it to the front-left of herself. When the camera switches to viewing her from behind and above, when she's looking at the button, the string is visible. The string is clearly too large for the box, it is still tied, and it is now directly to the side of her, instead of being in front and to the left of her, where it was tossed.