Thirsty Grunt
From Halopedia, the Halo wiki
In the Halo: Combat Evolved level, The Maw, immediately after the bridge where you see Foehammer go down, go into the tunnel to your right. And enter the room to the right of that. You will see a lot of bodies, and one live SpecOps Grunt. He will sit there, trembling, until you approach. He will look up and say, "Good thing that food-nipple's waiting for me at the starship 'cause man, have I worked up a big grunty thirst!" (listen) He will say nothing else and will continue to sit there unless you melee him. In this case, he'll scream "Oww!"
You can also run him over with the Warthog. His corpse will then rise into a standing position, and he will talk anyway.
Note that he is the only SpecOps Grunt in Halo: Combat Evolved who carries a Plasma Pistol, as all others in the game carry Needlers or Fuel Rod Guns.
Trivia
On the page for the Grunt water bottle at the Bungie store, the description mentions a "grunty thirst."
