: In the original Quarantine Zone final cutscene, it looked like Keyes grabbed
: hold of a Gravemind tentacle. I assumed it moved because the Gravemind was
: trying to kill her, and prevent them from getting the index.

: Now, its just a steel cable that slips. =\

: I guess she just gained weight over ten years.

Yeah, I noticed that too and was huh? I had figured that was how Gravemind knew that the Arbiter would be falling soon as he 'heard' what had transpired above him probably via the tentacle. I can't think of a reason he can't 'see' and 'hear' in some fashion from even tentacle appendages. When Keyes grabbed the tentacle, he was probably made aware that the Index had been found and extracted, leading to his speech to the Chief and Arbiter later.

Now, how would he know to catch the falling Arbiter?