Numb3rs (2005)

Alan Eppes: Ah, I'm just a little nervous.
Terry Lake: Don't worry-everything looks wonderful. In fact, your son could learn a few things from you. Know where we went on our first date?
Don Eppes: All right, all right, all right, all right.
Terry Lake: The laundromat. Dinner was pizza.
Don Eppes: A little professionalism.
Alan Eppes: You don't say... How interesting.

Thirteen - S4-E4

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.

In Plain Sight - S2-E8

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?