When the show opens, you see the table that Detective Benson is tied to and it is perfectly clear of anything. When Lewis turns the radio on to let the squad know that they are playing Russian Roulette and he is "Sliding the gun" to Benson, you can clearly see a white rope on the table.
In the very next scene, when she picks the gun up, the rope is no where to be seen for the rest of the show.