My original idea was to have one of those old fashioned sort of "Rube Goldberg" cartoon hands at the end of this long scissors extension thing, but after fighting with the rig for so long, I am not in the mood to mess with a hand at the end. Maybe later. Anyway, the large "red double arrow" thingy is a bone with a custom shape (and why Blender thinks it needs to be twice as long as the regular bone it represents, I have no idea...). In pose mode, if you scale this bone, it will work the scissors. Basically the bones for each "X" of the scissors are in a sort of "trident" arrangement. The middle bone (like the one you scale) has an empty parented to it, which empty is at the pivot point of the next "X", The two bone configurations on either side have an IK chain with the empty as the end of the chain. Scaling the bone pushes/pulls the empty and makes the bones on either side do their thing, thus working the "X" parts of the scissors. Clear as mud?