Special dialogue Grunt
From Halopedia, the Halo wiki
There are three instances of Talking Grunts to be found on the Halo series that have special monologues which appear in the form of easter eggs. The first is at the end of the level The Maw in Halo: Combat Evolved. When you are escaping the Installation in the Warthog, you will come to a large jump. If you exit your Warthog and walk to the end of a nearby tunnel, you will see and hear the Thirsty Grunt, if you keep walking you will see a blind grunt. The second is in the Halo 2 level Uprising. There is a live Grunt hiding in a corner near two Grunt corpses, known as the Cowardly Grunt. There is a third talking Grunt called the Final Grunt at the end of the level Halo in Halo 3, located to the right of the UNSC Forward Unto Dawn behind the end of a bridge of rock that you drive under. None of these Grunts will (or can) fight you, and will die like normal Grunts if you shoot them.
