In the steel mill scene, Arnold gets his arm caught in a gear where it is detached from his body. He walks away and the arm remains in the gear.
The main mission in the second half of the movie is to destroy all information, files, eveidence, etc. about the Terminator in order to stop the reoccurance of any of the hazardous events in the future and to stop any more Terminator creations.
They all went through a lot of trouble and harm to accomplish their mission, yet the arm(evidence)remains lodged in the gear. Seems all for nothing..it all can happen again.
Is this just means for another sequel, or just a slip-up. I guess we'll find out.