Throughout the film, the henchman Max wears two rings on his right hand. When digging near the end of the film, the rings switch to his left hand, then a few minutes later, they are back on his right hand.
When Dr. Conrad is on the phone with the kidnappers, he hangs up and throws the phone onto the bed. Yet when the kidnapper calls back and Dr. Conrad answers the sound of the phone being lifted from the cradle can clearly be heard even though the phone was not placed on the cradle.
The 2s Elisabeth writes on the glass with her finger are a different shape than the ones Dr. Conrad points out after they've dug up the wrong grave. His point was that she was writing it backward, but her 2s would not have looked like 5s in reverse.
When Detective Cassidy is questioning Dr. Sachs in his office, she is seen holding a photo of Sarah. When the camera angel changes, she isn't holding the photo. The camera angel switches back, she is holding the photo. This happens throughout the scene.
When they are driving the stolen boat to Hart Island they see the setting sun above the horizon. According to Conrad it is past 5:00 o'clock in the evening. On Thanksgiving Day 2001, the sun, at New York City, sets at 4:33pm. Even if it is not 2001, the sun would have set by 5:00 p. m.
The graves in the NYC Potter's Field are not marked with wooden crosses - brush fires in the early 1900s on Hart Island destroyed the wooden grave markers and after that the graves were marked by concrete and stone markers. Also there aren't individual markers for each grave, there are over 100 coffins per site.
Aggie's Apple notebook appears to have its trademark logo on the cover upside down. This is how the G3 PowerBook is designed and is not an error. Starting with the subsequent G4 Powerbook, Apple reversed the logo such that it's upright when the laptop is in use.
Near the end, Douglas holds a gun directly at Bean's head. In the close ups, Douglas's eye contact with Bean seems to be downward at about a 45-degree angle. But Douglas is standing and Bean is prone on the ground. Since Douglas is not on his knees and if we use Pythagora's Theorem with the angle of eye contact and the actor's 5'10" height; one must conclude that Douglas's left arm is over eight feet long.
The goof items below may give away important plot points.
In the final scene, when Dr. Conrad picks up Patrick's gun you hear the sound of the hammer being cocked back. When we see the close-up of the gun put against Patrick's head, the hammer is in the down position.
When Max is about to shoot Dr. Conrad, Dr. Conrad knocks the revolver off Max's hand. During their fight, Max never tries to retrieve the gun. Yet when Dr. Conrad kicks Patrick into the open grave, Patrick lands near Max's body, we can see the revolver is back in Max's belt.
At the graveyard scene, the doll wherein the diamond is hidden is shown in perfect shape. In reality, after 10 years in the churchyard soil, not much should be left either of the simple wooden coffin or of the cotton and wool doll.
During the shootout at the end, puffs of smoke enhance the effect of bullets hitting victims. However, a puff of smoke comes from Detective Sandra Cassidy before she's shot by the villain, Patrick Koster.