This trap involved a large glass container which was suspended from the ceiling in one of the rooms of the house.
Inside the box was an antidote which was accessible by two holes underneath the box that were big enough to fit a person's arms through. Once they did so, however, they would realize that the corners of the holes were fitted with blades that would push up if something was inserted and if the person put pressure on the blades in order to take their hands out, the blades would dig into their arms, and the harder they pulled, the deeper the blades would go. Addison fell victim to this trap. At first, she only inserted one hand, and may have been able to push open the blades with her free hand and release herself (cylinders extending downward from the holes in the box would have made this extremely difficult), but the plunger to the needle was stuck to the bottom of the box. When she pulled the needle up, the antidote inside spilled. Panicking, she reached her other hand inside to grab it, trapping herself.
As she tried to pull out her arms, the blades began to cut into them. It is later revealed in a featurette on the construction of the trap for the set that if the victim were to walk to the other side of the box, they would see a lock with a key sticking out of it, which in turn would have unlocked the box and allowed them to access the antidote without harm. If one looks closely enough during the movie you can see the key for a few seconds. Although Addison fell victim to this trap, it was intended for Gus Colyard.
Before deciding to place Addison in the Razor Box Trap, the creators and writers discussed on a commentary for Saw II that they had originally intended for Addison to end up in a different trap, which was similar to a waffle iron. It would clamp down on Addison’s hands when she reached for an antidote, and burn them until released. The only way to unlock it would be to apply pressure to the top, which would have to be done by her head, as both of her hands would be trapped. By pressing her face against the top, she would open the mechanism up, freeing her hands and escaping at the price of burning and scarring her face.
According to the commentary on the DVD for Saw II, the tape for Gus would have said something along the lines of him always "reaching his hand into the cookie jar for money," while Addison's would talk about her having to sacrifice her looks to escape her original trap. When Addison walked into the room, she found an envelope with the tape inside. Tearing it open, she found the tape for Gus, but tossed it aside, as she didn't have the tape recorder to play it.