When Chang's paint bomb explodes, the explosions can be clearly seen emanating from either side of the study room door rather than from Chang. Also, Britta is not visible in the shot even though she had been standing upright near Jeff before he ran.
When Troy is talking to Shirley about taking out the other 5 of the study group, the toothpick in his mouth appears/disappears multiple times.
When Britta is holding a gun on Jeff in the library, the gun is held sideways as the camera is looking at Britta, but upright when the camera is facing Jeff.
In the opening scene, Dean Pelton is standing at the table between Brita and Jeff. The camera cuts to Annie and when we return to the Jeff and Brita, Dean Pelton is gone.
When Jeff enters the first building after the nap, a person, possibly a crewman, can be seen sitting in the row of seats in the hallway to the right.