When Nikki and Willy hang out in private outside of a bar/nightclub, the former says to the latter, "So, I think you should go home," but there is a discernible delay between the actress speaking and the movement of the jaw and chin.
Towards the end when Beachum calls on Crawford, Crawford looks in a security monitor. Under the monitor there is a security panel for an alarm system. When the shot changes, the panel is gone, then appears again.
When Willy walks into his room, Nikki is just leaving him a message. Afterwards, when he plays his messages the machine says he has one new message and plays the call from Miramar left around 4.30 pm. There would have been at least two messages.
When Willy Beachum is rushing to the hospital to serve the court order, he is shown clearly driving on the 10 freeway and then exiting to go to the hospital. The hospital is St. Mary's Medical Center in Long Beach which is nowhere near the 10 freeway.
By the expert's testimony in court we are informed that Ted Crawford's bullet pierced through the frontal cortex in the temporal lobe coming to rest upon the upper side of the brain against the skull. Yet when we see wife Jennifer's head hit the floor for a brief moment in a close-up, there is no injury visible at all. Furthermore in another scene Ted points to his left cheek bone when he describes where he shot his wife. Such an injury is very different from that described during the trial. The shot was fired at close range with a powerful .45, which makes it very unlikely that the bullet would come to rest within the skull.
At the beginning of the movie when EMTs are working with Jennifer Crawford, they are heard saying "she has a pulse" and then administering chest compressions. According to BLS, when the patient has a palpable pulse, chest compressions are not administered.
All modern guns are test fired at the factory after assembly, to ensure they fire accurately and function correctly. Even if said gun was never fired by the owner, there is no such thing as a gun that has "never been fired".
In one scene, when Ryan Gosling's character is viewing the security video file on his MAC, he tries to zoom in to try to view the face of Anthony Hopkins's character. When he zooms in, the mouse pointer also gets magnified. Although the mouse pointer would not magnify if the application zooms into the image, the MAC OS also offers a 'zoom' that magnifies not just the screen, but the mouse pointer as well.
When the nurse removes the endotracheal tube from Ms. Crawford, you clearly see it was only long enough for the actress to bite down on it and missing several inches of tubing that should have gone down her trachea.
When Willy is reading Dr Seuss to Jennifer in the hospital and the nurse walks in we see the back cover of the book. The spine of the book should be pointing towards Willy's left side but it's actually pointing to his right. Thus, he's holding the book upside down.
The goof item below may give away important plot points.
When Beachum attempts to enter the hospital ward, he is restrained by two uniformed security officers, in spite of repeating several times that he has a court order from Judge Gardner preventing the life support from being switched off, and displaying the order openly. Crawford and his lawyer are also watching from inside. The lawyer and the security officers would surely have known that by preventing Beachum from executing the court order and by allowing the prevention to take place they were all guilty of contempt of court under section 166.4 of the California penal code. Also worth noting is that at the end of the movie, a fresh charge of murder is brought against Crawford after he switched off his wife's life support. This would have made the lawyer and the security officers accessories to first degree murder.