This mistake is after Jack gives Greg the polygraph test, the next morning, when Greg wakes up. The camera shows Greg sleeping and Mr. Jinx, the cat in front of him, looking at him. Nothing is behind, or near the cat, except for Greg, who is in front of him. In the next shot, the camera slides up from the cat to Jack, who is sitting very close to the cat, with is legs behind Mr. Jinx. Obviously, Jack wasn't sitting there before, because you would clearly be able to see Jack's legs in the previous shot. He could not have come in, because it was a matter of seconds between the two shots, and you would have heard him come in and sit down. Jack appeared out of no where! It's magic!