When the chandelier falls onto Lisa Sheridan, she appears dead, with her head turned towards her right. After the reaction shot of Sharon Daniels, the still "dead" Lisa Sheridan character is in the same position, but with her head turned towards her left.
When Derek is getting ready to go to the Christmas party and asks which tie to put on, after the selection is made, his collar is not on straight. In the next shot his collar is smooth, then it's not on straight, then it's smooth again.
When Derek first has Lisa sitting in his office and the camera view is toward Derek, a coffee cup is in his left hand. However, in the succeeding view looking toward Lisa the coffee cup is suddenly in Derek's right hand.
(at around 15 mins) During the montage, Derek is dropping off his son Kyle to the babysitter, as Sharon watches from the window. Derek is wearing a brown coat with a white t-shirt underneath. As he is pulling out of the driveway in his vehicle, he is seen wearing pin-stripped, button-up shirt.
In the scene where Derek and Lisa are eating at the bar before the Christmas party, Lisa approaches the bar and her watch is on her right wrist. When she is shown in later scenes, the watch is on her left wrist.
When Lisa breaks into Derek's house and wears his t-shirt, it is inside-out when laying on the bed (number 14 on shirt is backwards). When Sharon comes in, Lisa's shirt is right side out (number 14 is shown correctly).