Visiting a tibanna gas mine with a protocol droid is a dangerous thing
to do, especially when there are stormtroopers present. If your
droid should happen to get blasted into 4 parts, you may have trouble
re-assembling him without some Ugnaughts. In fact, the odds
against doing it successfully are approximately 3,720 to 1.
Depression of the round button on C-3PO's belly releases a spring loaded
mechanism which causes his arms and head to detach from the
torso. This is a touchy mechanism which can go off for no reason
and is somewhat difficult to assemble again.