As Mark crawls up to Romey's car from the right hand side, Romy sees him out of the right wing mirror viewed from inside the car from 06:38 to 06:40 on the DVD. In the mirror, Mark is crawling straight toward the mirror, while in previous and subsequent shots he is crawling to the back of the car from the side.
Mark's hairstyle when talking to the thug in the hospital changes from having the part on his right side at 45:21 on the DVD sweeping to his left across his forehead to having the part on his left side at 45:25 sweeping to his right across his forehead. At other points in the film, such as 28:51 when he first talks with Reggie, the part runs down the middle of his head.
As Reggie and Mark approach the boat house, Mark shines a flashlight from his car. The shot inside the car shows that the flashlight is emitting a bluish halogen light. From the outside, the beam is a yellowish incandescent color.
When Mark and Reggie hug while his family is boarding the plane to Phoenix, there are flipped shots where Reggie's bracelet swaps from her "right" wrist in close-ups of Mark showing her "right" hand is on Mark's shoulder (at 1:53:54 and 01:53:57 on the DVD) to her left wrist in her close-up where her left hand is on the back of Mark's head (at 1:53:56 on the DVD). This was done intentionally because Mark's head was actually facing to his left in his close-up but was facing to his right in Reggie's close-up; the flip avoids Mark appearing to turn his head during the hug.
Positioning of the Sprite can when Sergeant Hardy hands it to Mark Sway. It is in Hardy's hand, with the label to the left of his thumb (at 18:47 on the DVD), then he says its a Sprite, and the can is turned around in the next shot with the label to the right of his thumb (at around 51 mins).
When Romey locks the door as Mark tries to get out, he first hits the unlock button instead of lock at 07:17 on the DVD, and then locks the doors at 07:21, which shows the lock/unlock button on Mark's door moving from unlock to lock.
When Romey re-inserts the hose and handkerchief into the tailpipe (after Mark removed it) his fingers and hand touches the tailpipe a number of times. This is impossible without burning the fingers. Also, the handkerchief after coming out of the tailpipe is as clean as when it went in.
When the lawyer shoots through the side window of the car (at the beginning of the movie), the entire tempered glass window would normally shatter into small glass bits instead of well defined bullet holes.
Some have suggested that Mark could not be charged with obstruction of justice simply for lying or refusing to cooperate with the FBI, because of the 5th Amendment. This is not true. Lying to the FBI/prosecutor/police officer can result in a charge of obstruction. Refusing to answer questions will quickly result in a formal subpoena; if one then continues to refuse to testify, he could be charged with contempt. The right not to speak to police or prosecutors (the 5th Amendment) only consists of the right not to incriminate oneself of a crime. However, at the court hearing, Reggie tries to argue around this limitation by pointing out that the prosecutors vaguely implied that Mark could've been involved in killing the lawyer. But the judge doesn't buy it (and the prosecutors could easily get around the problem by giving Mark a guarantee of immunity). If he refused to testify, Mark could be charged with contempt of court. If he lied, he could be charged with obstruction of justice, lying to a federal agent, and/or perjury.
When Mark asks Reggie why her kids don't want to see her, she states that it's because after her divorce she drank a lot. However, she goes on to tell her story about what happened and that the court declared her unfit, and that it wasn't until after her kids were already taken away from her that she started drinking. How could her kids be around her when she was drinking, if they had already been taken away?