- last post: 01.01.0001 12:00 AM PDT
I have observed, that High Charity has a teleport grid. The Covenant may not be aware so, or they would've replicated the technology. That is why I believe the city of High Charity is a Forerunner City as a mobile battle station and haven from the Flood. If the Flood were to invade High Charity, then I suppose all would board the Forerunner Ship to evacuate. Cortana detects an AI presence aboard the Forerunner Ship, and this I believe to be a Forerunner AI who is the shipmaster. Any ordinary sentient being would eventually die, or wouldn't spend his whole life inside the ship, nor can a sentient pilot respond immediately in case of an outbreak. But an AI can do all these things, and Cortana was surprised how resilient it is while she tries to delay the launch(it is on a countdown?).
And Gravemind's teleportation ability. You might argue that he's half machine who's able to manipulate other machines(2401PT, Cortana), hence his metallic tentacles(Miranda must've mistakened it for a cable in the Library) interactions with AIs and subsystems as well as being able to hover and emit a mechanical pulse hum. If he can control other machines, then he could've used the teleport through 2401 just like half speaking through 2401 to get his point across to MC and Arbiter("Now I shall talk..."). But, if he can tap into the teleport grid directly, what's to say he can modify its circuitry or network to send MC and Arbiter away?