From Halopedia, the Halo wiki
- Arm it with a Okarda'phaa-pattern plasma rifle.
- Open up the piston and push him off, down to the first level.
- You can now melee it, and it will not flinch from attacks nor will show blood when fired at. You can throw grenades at it, but it will not die.
- If you kill any Constructors, the glitch will not work.
- This glitch can also be done by letting the Grunt activate the piston and then throwing a grenade at it.