Corrected entry: During the freeway chase scene in the helicopter, when T-1000 follows the SWAT car under the first overpass, as the T-1000 reloads his gun you can see a third arm under his own right arm flying the helicopter. When he flies over the second overpass and fires his gun, you can again see his left arm firing and another left arm beneath his own flying the helicopter.
Dandude776
4th Aug 2005
Correction: This mistake has been submitted and corrected many times, along with being listed in the trivia section. Since the T-1000 is liquid metal he could easily generate a third arm from out of nowhere.
Dandude776