I was combing Halo 3's website for new Iris details when I stumbled upon two interesting quote in the character section for Gravemind:
Sound familiar? "He has had millennia for reflection, but what image does he see," the late Adjutant Reflex once said."It is the flood personified, and it carries with it the genetic memory of millennia of slumber"
What other entities within the Halo universe do we know that have been around for millennia, would be around in the year 2007, and have had thousands of years to themselves? Of course, this could yet be referring to a monitor... however, the monitors most likely would never leave the Halo rings.
Next quote:
The comparable Adjutant Reflex line: "Something that was once malevolent is now stirring.""The thing was stopped before by the Forerunner activation of the Halo weapon."
Nearly 100,000 years after the Halos fired, wouldn't it be likely that the remaining Flood would be reawakening? Gravemind was once malevolent - as in, he posed a threat to the Forerunners/life in general - but was defeated by being sent into hibernation. In its hibernating state, Gravemind would not pose a threat to anyone (ONCE malevolent). Now, however, Gravemind is waking up, and Adjutant Reflex didn't want to be awake when he did.
Thoughts? I know this theory isn't foolproof by any means, but I thought it to be interesting.