Visible crew/equipment: After Charlie comes up with the idea of creating a false master key and designing the lock that it opens, when it cuts to them back at the office the yellow T-mark can be seen on the floor by David's foot.
Numb3rs (2005)
1 visible crew/equipment mistake in Prime Suspect
Starring: Judd Hirsch, David Krumholtz, Rob Morrow, Alimi Ballard
Continuity mistake: Around the middle of the episode, Charlie Eppes and Mildred French are discussing in front of a board. She completes an equation and he adds a minus. In the next close shots, the minus disappears and reappears with angle changes. After three or four changes, a circle appears around the minus.
Colby Granger: You assaulted a federal agent with a deadly weapon.
Henry Korfelt: It was a Volkswagen.
Trivia: The episode revolves around a man killing people with the same first names as the thirteen apostles (Mary Magdalene being the 13th), and killing them in a similar fashion in which the apostles died. At one point, Colby and David find a box with a mannequin's head in it. This is a reference to the film Se7en, in which seven people are killed for committing one of the seven deadly sins. The film ends with the main characters finding an actual head in a box.
Question: This question is about the mistake where a SWAT officer has a magazine backwards in his MP5. I know this would be impossible on a real weapon. But, how could it have happened in filming? Rubber cast weapon? Very badly worn prop weapon? Set armourer with a hammer and no clue?