Grenade animation glitch
From Halopedia, the Halo wiki
The Odd Flood Glitch can be performed on any level with Infection Forms and grenades in Halo PC and Halo: Combat Evolved. Basically, when the Flood Infection Forms are draining your health bars (i.e. when your shield is down), right before you die, throw a grenade. The camera will behave just like you died, but your body models completes the animation (and the throw) of the grenade being thrown.