When Hotch sends Elle home to sleep, Anderson puts his jacket on twice.
At about minute 30, when the team are in Frank Giles' bedroom and Reid is trying to recreate the 3pm shadow of the sword, the light reaches just above the line on the wall, with the shadow sword almost touching that line. When Morgan removes the table, the light and the shadow are considerably lower. In the close-up, when Morgan taps on the wall, the light again reaches just above the line, but the shadow is a good deal higher up, suggesting that the light source is positioned closer and with a steeper upward slant.
When Reid walks into the room where Frank Giles was killed, he takes his hand out of his pocket to scratch his abdomen, but in the next shot his hand is back in his pocket.
When Morgan removes the CD from the secret compartment the lock of hair is in it, even though we just saw that the hair was completely out of it, and Morgan even seemed to pull the last few strands away.
Elle was on two weeks vacation in Jamaica but returns after only one day to work on the case and goes straight to the office when she gets off the plane. She spends hours at the office and is then sent home for some rest. When she walks in her house, you can see two windows behind the couch are wide open. Presumably they would've been closed for her vacation, yet this does not cause her any concern.
A man can be seen in a mirror on the upper right of the screen when Elle walks into her house in the last scene.
When Garcia reveals that she knows who hacked her system - Frank Giles - she says he's in Arlington, VA, 4 miles from where they were. But the BAU is headquartered in Quantico, VA, 40 miles south of Arlington.
Hey, Derek. Most walls are hollow.
(at around 24 mins) Morgan, Elle, and Hotch get out of an elevator. As the elevator door opens, Hotch (in the rear of the elevator, behind Elle) is laughing hysterically, but quickly composes himself and emerges with his usual dead serious face.